There is little in the world worse than cat pee!!
Our cat (16 yrs old) began peeing on the carpet last year. No medical reason, just old, I guess. Once they have a spot, it is so difficult to get them to stop. If you clean the spot with an enzyme cleaner, make sure that you follow the directions to a "T". Douse the area, and keep it wet (cover with wet towels and keep the towels wet) for a couple of days to allow the enzymes time to work all the way down to the padding. It will
stink during this time!
We did this a few times and even then, she would be drawn to that spot. Now, poor old Blondie only has access to a couple of rooms upstairs. She has two litter boxes because her kidneys are obviously shutting down and she drinks and pees A LOT! Poor ol' gal.