Cats have an extraordinary sense of smell, which helps them in the wild, but it's very hard on the furniture when a male kitty can smell one part "tomcat" to a zillion parts of anything else.

It seems to me that oxygen cleaners are the best.

In my experience, once a cat does his business where he's not supposed to, he'll continue doing it forever in that place. It's impossible to get the smell out, and it's the smell that makes him go back and do it again. You need a new couch.