some bums in my neighborhood built a public "toilet" in a nearby intersection. its built up against a tree to hide it from public view.
It is constructed of pallets, zip tied and screwed together. inside there is a bucket, with a toilet seat.

I haven't been able to bring myself to use it yet.

Bah. How about a tarp, staked down over a hole dug into a hillside? Inside the whole is a wooden crate, with a supply of black plastic trashbags, each one containing a small handful of baking soda. That was the fancy toilet I had at a worksite 2 years ago.

See, the bucket is where they're going wrong. Nobody's emptying that. Just dig a hole, then cover it over and dig another. Maybe plant a marker so you don't re-dig your hole.