my dad got his car keyed in a quiet little close where we live, was expensive to repair it was the front wing and part of the drivers door on his XJ8 and had only been respayed earlier that year, but there was paint stored at the garage incase he needed any touch ups done, because the cars sliver and would be a pain to match up, but anyways he brought a CCTV camera from QVC i think off the tv (wasn't too expensive) but its set up to play on the tv up stairs in his room and the camera rotates and looks at the cars on the drive, hehe got a CCTV sticker stuck on the front door window, havent had trouble since.
but end of the day buying a little camera is cheaper than paying to repair your car a few times.