I assume that if you bury a box of any size, you disturb the ground quite a bit. You also probably don't bury it in a random open field but near some landmark you can easily locate.

Yeah pretty much exactly this.

There are signs and landmarks. Trees, stumps, rocks, corners, etc.

Sometimes people make a mark to make it more recoverable, like a notch in a tree, or a topped tree.

Especially when a big part of my job is figuring out what the terrain and vegetation looked like before disturbance for restoration work. I can see 30-100 years of history by looking around or reading old surveyors descriptions and stuff.