A way around the ground return problem (and the spark damaging the paint) would be to run a few parallel strips of aluminum foil over the roof/hood and electrify that, not the car. 230V would be perfectly adequate, considering it would have a nice chance of following a "front paw - body - rear paw" path.
If I get 'round to installing the motion sensitive sprinkler, I may as well just electrify that instead
