Google for bacterial(enzyme) solution against piss smell.
Wors then human piss, is cat piss. I have 4 of them. I buyd 2 years ago a new couch and one of my sweet cats

is pissing on my 7000 dollar couch. I was trying alot of normal liquids, you can buy in thewalmart etc. nothing helped.than i found an special bacterial solution which helped me 100 %. After the threatment with this liquid, and wait +- 2—3 weeks, my couch is like new. I was very skeptical to, but believe me, this was the only one so,ution for me. This liquid was maybe 20 dollar for 1 liter.
Something like this will help you for sure:
http://xionlab.com/enzyme/