Man that sucks. Sorry to hear it. We had a bunch of kids doing that around here. I got lucky and never got hit, but a few people that live next to me did.
After I was hearing about all the goings on I wanted to contact this company and see if they could incoporate their design into car security.
http://www.pimall.com/NAIS/shockalarmbriefcase.html
I know bad time for a joke, but sometimes it helps.
Good luck on the repiars.