A friend of mine used a thunderflash type thingy to deter unwanteds, but forgot it and set it off himself! Scared the living daylights out of him!
We've put up a camera and (so far) it has been very successful. We even had one lot of fly tipping b@s!@rds who went down the lane and regularly chucked out slabs of stone all the way down except where the camera would have caught them! Although to be fair, we also sit outside from time to time when we have a spate of fly tipping in particular, as they seem to follow a particular pattern.
Horrible feeling when someone nicks stuff from you though.