I had the same issue with my ibex- skin was tanned at a commercial, top notch tannery but it still a slight "urine" smell after the tanning process. I shampooed the cape prior to mounting, let it dry out after mounting but still had a slight odor. I tried Frebreeze, followed by dusting with baking soda without much success. An old-timer taxidermist told me to sit it outside in the sunlight for brief periods at a time (usually direct sunshine on a mount is highly discouraged). That seemed to help and the old-timer claimed the sun's UA rays broke down the urine- not sure but it did have some positive effect I felt. I next tried a commercial taxidermy deodorizer- that had it's own particular smell. Not sure the urine smell wasn't better
Long story short- although I did have some effect on reducing the odor, you probably don't catch a slight whiff until 3 ft away from it now, I haven't been able to
fully eliminate it.
NOW FOR THE KICKER- despite all the effort, I'm still highly ALLERGIC to it and can't be in the same room with it, even hung 15 ft up and across the room, for over 30 min before my chest starts burning, throat gets scratchy and ears begin hurting as if I have an ear ache. It's one of my favorite animals and a 1/2 lifesize mount and I have to keep it in another room with the door closed !! It's been put away for 2 yrs now and every time I bring it back out thinking I'll be ok- I start reacting again !