My guess is the dog is trying to make his spot comfortable, my dogs do this, scratch the surface before they lay down. I'm stumped as to what to do with the bed, but do you think if your son got the dog his own dog bed he would rest there instead? It would also help if he trained him not to go on the bed when he is home. There is a chance even in his absence that he will not go on the bed any longer at all.