You can also purchase, from hunting stores like Cabela's, motion detecting digital cameras. Normally these are used for photographing game animal trails, but there is no reason they couldn't be used to photograph folks who pee on other people's porches -- or trespass, or peek in windows. And take it from one who knows, cops LOVE good clear photos! Just be sure to hand the undeveloped film (if film is used) to the cop and get a receipt for it -- that preserves the chain of evidence. I suspect a nice printout of a digital photo would be acceptable in court as long as you didn't offload the picture from the original camera.

Some examples are here.