I know I bang on about it a lot, but try Zylkene, It's a milk protein based vet recommended product that you open the capsules and mash it into wet food, it helped a lot with behavioural problems with my latest rescue. Also try using an enzymatic cleaner, PAH sell it although I am a lazy cow and can't be bothered to drive that far so I get mine from my local Vets, by the time I have paid for petrol it's probably about even. Ordinary washing will kill the smell for us, but cats olfactory organs are so much more sensitive. You can also get the Pet Rescue and Feliway diffusers. I hope that helps, along with maybe treat balls that he has to work for to keep him occupied?
