And finally I recommend you not bury anything of value in an area outside your watchful eye or control. Especially a firearm. Ammo maybe.
Yea, I have a bit of an issue with that too. Burying it in your basement or putting in your walls is one thing, but outside there are just so many bad things that could happen. I'm assuming its on your property. Burying an AR and ammo on someone else property or on public land would be downright stupid, and illegal.
If you put it outside, even on your property, it could be;
Dug up and stolen in the middle of the night.
It could be destroyed by the elements, just a pinhole leak and the contents of that box could be ruined.
Most of all, if you God forbid die suddenly and not tell anyone the location of that box,it will never be found. Your relative would miss out , and you could have complete strangers find it down the line, and use it for bad things.