I recently took in a cat from a friend. He used to be indoor/outdoor and was not given regular access to a litter box inside. He's now completely indoors and he's so well behaved...except for one thing. When he uses his litter box, he digs as deep as he can, makes his deposit, and proceeds to spend a good ten to fifteen minutes "thoroughly" burying his treasure. I use quotations because he obsessively digs so much that he flings litter and, somtimes poo, everywhere. He often gets it on his paws and at night the obsessive scratching at the litter box drives me bonkers. I have a self-cleaning litter box so it can't be that he's angry that his box is dirty. It seems like he is neurotically trying to cover up his smell. No other cats use his box and he's been here a month and seems to feel at home. Why is he doing this? He's making a mess! Does it have something to do with his past experiences of being left outside or not being used to a litter box? What can I do to fix this issue? How can I get him to just do his business, cover it up, and move on?