It's a matter of law (Road Traffic Act 198

in the UK that a dog cannot be on a designated road without it being held on a lead. Some local authorities have similar byelaws covering public areas, which would include parks and schools etc. I don't know whether this would apply to a school car park in your area but given that there are likely to be loads of kids then I would bet that dogs have to be on a lead. the best thing for you to do is complain to the school about uncontrolled dogs in the car park. Even if it had been on a lead when it damaged your car you have a case to say that the owner wasn't in adequate control of it because it was able and cause the damage - if you make a fuss then the school will have to do something.
I don't hate dogs. I love dogs, it's their owners I hate.
Too many dog owners just do not know the law or do not care to abide by the law. The dog is not technically responsible for the damage to your car, the owner is (under the law they may as well have scratched your car themselves), so it's a pity you can't track them down.
I was in a car park the other day when an old banger reversed into a space next to me (far too close by the way). After parking up the owner saw me and tried her best to avoid knocking her door against mine when she got out but failed miserably and looked fairly uncomfortable as she got her dog out of the rear of her car. There was no damage so I didn't feel too bad - I just wish she used her common sense and parked centrally in her space (or even in one of the many other empty spaces with no cars adjacent to her) if she wasn't going to be able to get out easily.
Anyway, the dog was in the back of the car, she opened the rear door and the dog bounded out running around my car with it's tail banging hard against my paintwork as it went. It then went out into the car park itself with the owner trying to get its attention to put its lead on. WHY didn't the owner do that BEFORE letting the dog out of the car?!?!? I politely gave her a few words of advice, pointing out that she parked too close, dinked my door with hers and let her dog add bang against the car and run around uncontrolled. Let's just say her response was less than friendly. I was apparently being unreasonable.

Hmmm.
Since that incident I have found a black scuff on the paint above my nearside wheel arch which must have been left by a van or something (not as bad as Lehn's but bad enough). Whenever I can I make the effort to park my car away from others in a sea of empty spaces and almost always some arse comes and parks right next to me. Why is it that nobody apart from me seems to want to park on their own? Are most drivers really so bad at parking that they HAVE to line up against somebody else at all times????
/rant.