Cat spraying

Hey guys. So I got my cats (both 2 years old) fixed this past week. There was a problem with spraying before and I guess they are still spraying in my FIL closet. They don't really go anywhere else. He has a small yippy dog that barks at them all the time and I'm thinking this MIGHT be why? I'm getting a second litter box today, my vet actually said not to try things like feliway because he said they don't work. Any other ideas on how to deter them from doing this or is it just not going to stop? Maybe their testosterone hasn't dropped off yet?