I bought a car seat cover for my Honda Accord at PetsMart over a year ago. I can't remember what make it was but this looks like it and the description matches
http://www.petsmart.com/products/product_21379.shtml
It has been great. Between my two girls, I probably have 150 lbs of dogs jumping in and out of the car. It has held up really well and there aren't any gashes or scrapes on it. The girls quite often are wet and/or muddy after their run in the fields/woods and dampness has never leaked through. I can't say how it would hold up to a soaking wet dog, but it does say it is waterproof. The price was definitely right as well. It isn't real fashionable, but it sure does the job.
We still have the Honda, but we recently bought another car, a Pontiac Vibe. I bought the same seat cover for it but it just didn't work out. :( The rear seat has quite high head rests and I found that the seat cover, although it fit over the head rests, just blocked my rear vision too much. I'm not real good at driving with "mirrors" when I back up, so I need a clear view. The back seats fold down flat to enlarge the cargo area and I found that the PetsMart cover really impeded this. I bought a different brand from Canadian Tire (which you probably don't have in the States) and it hasn't held up anywhere nearly as well as the PetsMart one has.