We've lived on our land for 7 years and all we have in an outhouse. We dug a new hole when we first moved here and moved the outhouse over it. About 3 years ago we dug another new hole and moved the building. Now most of the kids have reached adulthood and moved out, so it's not filling as fast.
We leave the door open when no one is in it. (It faces a direction where it's not an eyesore!) That keeps it aired out, in addition to the vents. It also lets us know at a glance if it's occupied. Another plus is that it keeps mice and packrats from setting up housekeeping, though around here people keep their toilet paper in mouse-proof containers (metal cans, usually).
Since most people in our neighborhood have and use their outhouses, we all decorate them nicely, paint them a light, cheerful color, hang pictures (humorous, if possible!), and keep entertainment there. One friend has an etch-a-sketch in their outhouse!
The top couple feet of our ground is rocky, and under that it's a gravely clay. Our hole is 5' deep. My husband has talked about doing the double-chamber style of outhouse where one side is composting while you use the other. By the time the other side is full, the composting side is ready to be cleaned out and distributed.
Milwaukee, Wisconsin has (or had, back in the '80s) a product called "Milorganite", and it's composted human waste, bagged and sold at garden centers such as Stein's. I don't remember if they had a warning on it about whether it could be used on food-producing ground, or just flowers.