I'm sorry to hear that you're having this problem. I would also try using Cat Attract Litter by Dr. Elsey which you can buy at Petsmart to see if this will help him start using the litter boxes again. When I had a similar problem this really helped me and I also added a few more litter boxes in different locations. My Storm is going to start taking Prozac because he's still aggressive towards his siblings and has become much more grumpy lately. I tried Clomicalm but it didn't agree with Storm and it made him too sleepy and lethargic plus he hated the taste. Luckily I don't have problems with spraying or peeing outside of the box any more. Good luck.