Bunker (left) and Woodson
I've never known a collie who doesn't sleep on it's back.
I'm sure other dogs/breeds do this, Brett doesn't. He likes to sprawl on his stomach kicking his hind legs out behind him.
We made a really quick trip to the dog park after picking KJ up from work and before the board meeting. Bunker got humped by a rottweiler and he stood there growling until the owner pulled his dog off, but did not fight.