I had a kitty that would use the bathtub as the litter box. He would poop right over the drain. I put "Comet" cleanser there a few times...and he would not like the smell of it. Then I would think all was fine...and sure enough....he would use the spot again....he would even do this at other homes we visited. He was probably a good kitty to toilet train...but I never thought of it then. He continued with this habit until he expired, 18 years later. Cleaning a tub is much easier than cleaning a sofa.

I too would either get rid of the sofa or cover it with foil for awhile...but I think getting rid of it might work better. Could it be that another animal urinated there some time ago?

Good luck with your kitty!