I like to discourage theft on the server I play by making a community junkyard. The basic idea is that every old time player discards stuff in there instead of lava-ing it, and then the new players dig through it for the good stuff.
This, hopefully, lowers the amount of theft. So far its just been a series of chests stacked all over. However, this time I was interested in making it an actual, proper junkyard. Like, with stacked cars (that are run down), fences, a car compactor etc. you get the idea.