L.H.
Go to petsmart or a similar place and buy some "Simple Solution" and drench your couch with it (It smells like baby powder which is one reason I like it better than other similar products made to remove pet urine smells/stains.. It costs about 16.00 for a gallon of it. It works well for moldy smells and all pet stains too. You can get it in smaller amounts. Depending on how far the urine seeped in and how much there was you might need a gallon though. It can take up to 6 weeks to totally get the smell gone but it works.
Good Luck.
L.