My male cat is 6 years old and we had him neutered when he was about 6 months old. Unfortunately, he has never stopped marking in our house and now it is getting excessive. Is there anything that could help him be more comfortable or relaxed so he wouldn't spray everything? We thought about trying Feliway diffusers but they are pretty expensive. Also, is there any chance the vet may not have done a thorough job when neutering him? Thanks!