I highly recommend a dog hammock. The picture shows you what it looks like but it's great because it prevents your dog from falling into the footwell, keeps fur contained, and helps keep them from intruding too much into the driver's area. You can used the rear footwells for storage and items are protected from drool and dog paws. The one pictured is the one I got. It's excellent quality and priced reasonably. We use it with our Rottweiler and in our Audi A6 Avant and the X5.
Installation takes a couple of minutes and one side can be zipped open for a passenger. This one is reversible with gray on one side and tan on the other.
Pet Squared Dog Hammock