$15,000??? Are you sure? My rotty had a ruptured cruchet ligament (from my mastiff jumping on her when playing

) and that was going to be around $1500 at most for the surgery.
I'd definitely install a security camera. Thats a great idea. Maybe you can pretend to go out and catch him on tape etc. That way if he does go to hurt your dog you can run out and stop him before he does but you've still got him on tape in the yard about to hurt him. And jut try to keep your boy inside whenever you can.
I have a neighbour with an awful kid who was always throwing things over the fence at the dogs. I talked to his parents so many times. Some of the things he threw at them were quite dangerous.
I made police reports several times. Even if they couldnt do anything, at least if the kid got bitten one day they had records that he'd been harassing them. I also kept my own records of every time I found something in the back yard and saw the kid on the fence or anything.
Police reports are always good to have, even if it's just for records. You never know when you may need to refer back to them.
And keep a record/ list of everything you can think of to do with him.
GOOD LUCK!!!!!!!!!