around here all you need is a warning sign, same goes for shoot-on-sight. If you have that on your fence and someone tresspasses, you can shoot him. (yay for michigan militia)
Either way thought if its a remotely controlled device, you can't argue for public endangerment or such. If the thieve coutner-sued the owner around here, it would get thrown out right away. Assuming you can prove that he is a thief