As a general rule in my travels is I do not plant on NP property, though as some of you who have found my NP themed boxes they may be right over the boundary line (Zion, Bryce, Capitol reef, fossil butte) and some of those you have to drive through he NP to get to non-NP public land. I have found a few boxes on NP property but I doubt they were placed there with permission. Only one in CO, was at the visitor center and you had to ask a ranger. As eidolon said, you would need permission from the park manager otherwise.

I did not find this to be the same in Canada parks though.

What are Canadian rules?

So I couldn’t find anything specific to letterboxing but here are the geocaching rules. Similar, but in my opinion a little more liberal than the US National Park regulations, or that just may be my interpretation, but I’m not a lawyer, I’m a dawgdok.

https://www.pc.gc.ca/en/docs/pc/guide/geocache

I've been boxing for 12 years, and have always gone by the philosophy of "what they don't know wont hurt them."

As long as the box was just off a trail, or in a safe area I would look for it . . . heck, I'd even plant one there (have to make sure the clues are cryptic enough not to pop up on their searches).

However, if a box is WAY off the path, in an unsafe/fragile area, I'd stay away.

hx6

Thanks! This is a very educational topic!