is it possible maybe to take his bed away during the day? you don't want him to get into a habit like that. I had a rottweiler pup who used to do that...he would be standing there...looking at me...and pee on his bed. This dog turned out to be very dominant etc with big problems. I am not saying your dog is dominant...it might just be because he can't hold it. My rottweiler had been allowed to pee on blanket etc at the breeders place, so it was a habit that took some time to eliminate.