Dachshunds licking the seats...

I have 3 dachshunds that just love going for a car ride in the Prius. As soon as they get in, they just start licking away at the seats. We didnt spill anything on them because the dogs lick EVERYWHERE. The seat backs, bottoms, headrests(when sitting on someones lap), and even the door fabric. They have done this ever since we bought it brand new in 2008(now at 10x,xxx miles). The seats have the dark gray fabric on them. Has anyone else heard of this? I cant seem to find any cases of it by looking it up. We have been wondering about this for years, iv just never asked about it. We swear we are about to call Toyota to get a good laugh about it. Thanks.