Okay, I think that this is the right board for this since this concerns hiding a letterbox.

I want to hide a letterbox in a location where a geocache has gone missing a few years ago (and been archived). It was an ammo can in a semi-wild place and it went missing before the trail was made past where it was hidden. I'm thinking that some kids from the nearby (less than 1/2 mile) neighborhood came here to play and found the geocache.

My idea is to make a small log into a hiding place. For reasons which are relevant to the idea I have for making this letterbox more interesting, I want to put a lock on this letterbox. I will drill a circular hole with a hole saw or forstner bit. I've done this before so this part is no problem.

To keep the lock protected from the elements as much as possible, the lock will be inside of the log. Let me illustrate my idea.

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|   | Contents  +-----+       +-----+
|   | Contents  |  2  | L     |  1  |
|   | Contents  |  2  | O     |  1  |
|   | Contents  |  2  | C     |  1  |
|   | Contents  |  2  | K     |  1  |
|   | Contents  +-----+       +-----+
|   +-------------------------------+
|                                   |
+-----------------------------------+

The "Contents" includes the stamp, logbook (depending on which box), directions to the next letterbox and its combination. The combination is used to make this letterbox series a set of field puzzles. Barrier "1" is to protect the lock from most of the elements. I'm thinking that I'll attach a wood plug to the lid of a salsa bottle so that it can be screwed on and off.

Barrier "2" needs to be lockable. However, all of the ideas that I've come up with have a problem.

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|   | Contents  +-----+       +-----+
|   | Contents  |  2  | L     |  1  |
|   | Contents  |  2  | O     |  1  |
| []=======================    |  1  |
|   | Contents  |  2  | C     |  1  |
|   | Contents  |  2  | K     |  1  |
|   | Contents  +-----+       +-----+
|   +-------------------------------+
|                                   |
+-----------------------------------+

I can use a bolt through the "Contents" portion with a hole in the end for the lock to go through. This will hold barrier "2" closed. However, because the bolt goes through the center of the space it will limit the size of items that can fit. (The head of the bolt will be covered by a plug so that it isn't visible from the outside.)

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|   +------------------[]-----------+
|   | Contents  +-----+[]     +-----+
|   | Contents  |  2  |[] L   |  1  |
|   | Contents  |  2  |[] O   |  1  |
|   | Contents  |  2  |[] C   |  1  |
|   | Contents  |  2  |[] K   |  1  |
|   | Contents  +-----+[]     +-----+
|   +------------------[]-----------+
|                      []           |
+-----------------------------------+

The other option is two rods across barrier "2" with holes so that they can be locked to each other. The problem that I see with this is that the holes will eventually be enlarged enough that the barrier can be removed even without unlocking the lock. The longer the lock's shaft the sooner this will happen. The longer the holes and rods the longer this will take.

Other ideas I've come up with will block barrier "2" from coming out.

Can anyone come up with some way that will work?

Make 'Contents' and '2' a single lockable cylinder to slide out? Hope you find an answer - concept is wonderful!

This is way beyond me.

By lock, do you mean the seeker has to look for a physical key? Metal key? Or a number padlock?

ok, I see you use the word combination, so it must be a combination lock. Maybe not the big horeshoe shape I was imagining, but a smaller cylinder shaped lock.

It sure sounds interesting!

Make 'Contents' and '2' a single lockable cylinder to slide out? Hope you find an answer - concept is wonderful!

This is what I came up with from your idea.

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|   +-------------------------------+
|   | +-         -+-----+     +-----+
|   | | Contents  |  2  | L   |  1  |
|   | | Contents  |  2  | O   |  1  |
|   | | Contents []=========  |  1  |
|   | | Contents  |  2  | C   |  1  |
|   | | Contents  |  2  | K   |  1  |
|   | +-----------+-----+     +-----+
|   +-------------------------------+
|                                   |
+-----------------------------------+

Then there would be one or more horizontal bar that goes through the bolt. This/these horizontal bar(s) are locked in place with the lock. This is a forward movement but may have the same problem.

I also have another concept from what you said.

+--------------------------------|--+
|                    \           |  |
|   +-----------------\----------|--+
|   | +-         -+----\+ L   +--|--+
|   | | Contents  |  2  \ O   |  1  |
|   | | Contents  |  2  |==   |  1  |
|   | | Contents  |  2  |==   |  1  |
|   | | Contents  |  2  / C   |  1  |
|   | +-----------+----/+ K   +--|--+
|   +-----------------/----------|--+
|                    /           |  |
+--------------------------------|--+

Nails hold "1" in place (rather than being a screw lid).

There are two diagonal rods that go through the cap of the "2" container (at steeper angles than shown here). Small washers could be used on the edges to keep the repeated insertion/removal of the rods from wearing the wood.

Here's another idea that developed from your input.

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+--------------------------------|--+
+-----+-         -+-----+     +--|--+
|  2  | Contents  |  2  | L   |  1  |
|  2  | Contents  |  2  | O   |  1  |
|  2  | Contents  |  2  | C   |  1  |
|  2  | Contents  |  2  | K   |  1  |
+-----+-----------+-----+     +--|--+
+--------------------------------|--+
|                                |  |
+--------------------------------|--+

The log is hollowed out the whole way through. "1" is held in by nails again. It conceals the lock which can be locked with a hasp. Since "2" moves the other way, the hasps don't have to get out of the way. The only problem that I see with this is that this gives two openings that could be seen by a muggle who would investigate. However, since "2" doesn't have to come out through the same opening as "1", "1" doesn't have to be round any more.

I think that these could work, but I'm still looking for more ideas.

Of course, the box doesn't have to be in this form, but it will have to be lockable and look like it belongs amongst the trees and undergrowth.

By lock, do you mean the seeker has to look for a physical key? Metal key? Or a number padlock?

You already answered your question, but I want to answer as well. Right now I'm thinking combination, but a clue could also lead to a key hidden in a letterbox or hidden elsewhere. There are really a lot of possibilities here.

The locks would be small one like these.

I assume that this is operating on the premise that locks are good to keep out honest people. A malicious individual could steal the entire log or defeat the locking mechanism by sawing through the wood.

So given that, you could use a piece of clothesline wire for the lock. Drill holes on opposite sides of the log, wrap the wire halfway around the log and in through the two holes and make loops on the ends of the wires inside the log using ordinary crimping clothesline fasteners. The padlock goes through the two loops, securing the payload in the deep end of the log.

(This would involve camoing and securing the wire on the outside. The alternative is to have two short pieces of wire, each secured on the outside but that seems to me to be a bit less robust than having a single wire.)

I assume that this is operating on the premise that locks are good to keep out honest people.

Correct. Making it look like something uninteresting is what keeps it safe from muggles. And the general trustworthiness of letterboxers is what keeps it safe from them bypassing the locking mechanism.

The padlock goes through the two loops, securing the payload in the deep end of the log. [...] This would involve camoing and securing the wire on the outside.

Good idea. This would work with any of the configurations. Putting the log wire-side down will probably be the best way of camouflaging it, especially if it is among some other logs.

It is a wonder what explaining something to someone else will do. I've had this idea for weeks but couldn't come up with an acceptable way of making this. Now less than a day I've got a few ideas, including the one that I'm replying to.

Here's another idea that I have.

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+-------------------------+    +-----------+
+-----+-         -+-----+ |    |     +-----+
|     | Contents  |  2  | |    | L   |  1  |
|     | Contents  |  2  | |    | O   |  1  |
|     | Contents []================= |  1  |
|     | Contents  |  2  | |    | C   |  1  |
|     | Contents  |  2  | |    | K   |  1  |
|     +-----------+  2  + |    |     +-----+
+-----------------------+ |    +-----------+
+-------------------------+                +
|                                          |
+------------------------------------------+

The lock is accessed from one side so it doesn't matter how big the hole is or how it is held in as long as the lock can be manipulated. However, for practical purposes, one must be able to reasonably get in there. I figure that if it is comfortable for me to do it with my big hands then others should be able to do it.

The contents portion needn't be circular, but it will be easiest to do so. It can be secured with a regular lock or the clothes line that you suggest. Either way the bolt will have to be thick enough to drill through for the lock's hasp. It could even be a strip of metal with a hole drilled in it.