How do you guys keep your pets, especially cats, off your cars during in storage? Don't get me wrong I like my wife's cat especially for mouse control. He eats them up like M&Ms! But the down side is he's always on top of the P-cars and with dirty paws. When he gets down he slides off the back or down the hood. I don't want to frighten him cause then the claws come out and SCRATCH!

I've already seen him scratch the car once that's why I won't scare him anymore.
He goes on the car with or without the cover once in a while. If I put a thicker one on there he likes it even more!
What do I do?