How old are the stains? Do they smell?
For new stains that are still wet, blot up the urine, then use some water to rinse it, then finish out with pet enzyme or vinegar pour on top. If there is any discoloration, use carpet cleaner, preferably the kind with oxygen bleach.
For recent stains that have dried follow the above as well, except, of course, you can't blot up any urine.
For stains that were missed and are older, use straight vinegar on the spot. Wine vinegar works best, but white works as well. Then use carpet cleaner to get out any discoloration. I had a spot recently (under a plastic table cloth that sits under a cat litter box) and no idea how long it had been there (at least 3 weeks). I carpet cleaned the area, used spray on carpet cleaner and scrubbed, then enzymed it. Still the smell persisted. Poured straight vinegar all over it and waited. As of last Saturday, the carpet smells of vinegar and nothing else when I put my nose to it, but I can live with that.