"The problem with cats scratching the car paintwork isn't when they climb on, but when they SLIDE OFF."

Well, I suppose they could ding the wax doing that. Better get one of those extra-hard wax jobs.

The problem here is that the cats have been permitted to be on cars for a long time. They have learned that lying on the car is warm, safe, and provides a good vantage point from which to survey their world. This is not going to change.

Dazbo should either quit worrying about it or find a garage.

By the way, I agree fully with those who say the cats should be kept indoors, both for the sake of the cats and other animals, especially birds.