Security lights can be angled higher than the dogs at the fence top so the only thing that would set it off is cats or people and I doubt cats would want to go by your dogs. Pigeon deterent strips can be put along the inside top of your fence. Letting the neighbours know about it should give you plenty of extra eyes especially if they have been in other peoples gardens already. The guy that sold the car is supposed to keep the details of the people he sold the car to so I would ask the police to contact him. It could be he knows the guys and doesn't want to tell you.