Game cameras, placed stratigically around the borders,(preferably aimed at the NO TRESPASSING signs, seem to work very well. They will record the time, and date, as well as a great picture of the trespasser. Since most of the time, we know who he is, we mail them a copy of the picture, along with a nicely worded letter, that explains we have sent a copy of the picture to the sherriff's department, as well as the local game ranger, and have asked them to keep an eye open for tresspassers. This seems to work well, because you hardly ever see them again. ( Don't sign the letter, and the trespasser has no idea who sent it. All he knows is that he got caught.)
Place your cameras in a well hidden location, and turn off the flash, since most trespassing happens during the day. This will keep anyone from shooting them or stealing them.