If it were me, I'd chuck it and get a new one. (Or check out some of your local kids resale shops. I've always been able to find really good deals on very gently used baby equipment.) We've had dogs in the past and urine is one of the hardest smells to get rid of. But if you want to try to salvage it, take it outside and spray it down with the Resolve pet stain cleaner. Then hose it down really, really well. You don't want to leave any chemical residue or fumes. Then I would invest in a few of the playpen sheets and a waterproof pad, just to be on the safe side.