I've had my cat for about four months now. When I got him he was already potty trained and was very good about using his litter box and covering it. Lately he has taken to not covering at all. He will get out of the box and try to cover it with the newspaper surrounding the box. I've tried putting him back and making him clean up but he just doesn't. I don't know what to do or what made him change his behavior. Any ideas?