Keep your car professionally waxed and then buy a tube of that miracle minor scratch repait stuff they advertise on TV here in the US. One tube for $20 will last you the life of your car and it really does buff away minor scratches as if they were never there. I wish I could recall the name.. GS7 maybe?

We went through a period qwere a gang of feral cats were hanging out on one of our cars hen it was brand new and all they left were dusty foot prints all over every horizontal surface. The minor scratches always came from people in parking lots ramming grocery carts into the doors or opening their door into ours.

Other solution - if you know the owner of the cat, offer to pay to put a product called "Soft Paws" on them. They are clear or nicely colored plastic claw sheaths that are glued on by the vet. they last a very long time and do not harm the cat. Outdoor cats usually only get them on their front claws so they can defend themselves with their hind claws if getting into a runble with other cats.