I have the custom covers from these guys
http://www.caninecovers.com/ for my CTT and the wife's Lexus. A little pricey, but they are extremely well made and have custom cut-outs for the seat belts. Their pattern for the Cayenne apparently is not cut for the soft-leather seats: the seat back portion is secured by velcro straps, which were too short. I emailed them and they custom-made some extension straps and sent them quickly. They also sell little panels to protect the door panel, held in place by plastic strips that slide down inside the window. They are less effective than the seat covers, but they help.
The only thing left is to replace the Vader costume with a suitable harness to anchor to the seatbelt, to protect the precious pooch and keep him/her from becoming a deadly (and likely dead) projectile in the event of an accident. And, of course, we never let our pups stick our heads out the window, do we? Lots of risk for ocular damage, especially for the brachycephalic breeds like pugs.
Can you tell my dogs are spoiled?

Happy motoring to you and your Top Dogs.