I just know there's an old thread on this, but for the life of me, I can't find it.
I wanted something so I could bring the dogs in the car, protect the upholstery, and that would also prevent them from popping into the front seat the second I left. The cover should be lightweight so as not to take much room when not being used, protect the plastic bits from claws and be washable. What I wound up doing is getting a 2-yard length of 60"-wide washable wool felt and punching some grommets into it. I painted some stick-on hooks black and attached them to backs of the front seats and at the front edge of the rear windows. The rear of the blanket can be fed between the rear hatch shelf and the saddlebag, or laid on top of the shelf with the lift cords threaded through, or laid flat on the floor so dog leads can be clipped to the back. The whole set-up works with the rear seats folded or not. Between the front headrests I have looped some black elastic which holds up the felt enough so the dogs can't come up front.
One additional benefit is that I can slide all sorts of cargo underneatch the felt and you can't see it from the outside.
Here's a picture: