Pet urine in the carpet is one of the most difficult challenges a professional carpet cleaner can get. I run into these jobs all the time while working in Tampa FL. Pet urine cleaners come in many variations but they all share the same common flaw. They rely solely on Enzymes to remove the offending pet urine smell. Enzymes can be effective if they are used when the urine deposit is recent and still wet. They also have to be applied in large amounts. If your pet urine cleaner comes with a trigger sprayer then it is going to limit how much of the enzyme cleaner is going to get where it's really needed, in the carpet pad.
So, what is the best carpet cleaner for pet urine? The simple answer is water. It's very effective at rinsing out pet urine. You just need to apply a lot of it while the urine spots is still wet. When my dog has an accident on the carpet I get a towel and soak it up as quickly as possible and then I poor a large amount of cold water on it, about 32oz (4 cups). After about 30 seconds I start to soak up the urine with a fresh towel. I keep blotting the spot until no water seems to transfer to the towel. Then I stand on the towel for another 30 seconds to soak up any last bit of it. About 95% of the time this takes care of and odors or discoloration.
If the urine is already dry then it's time to call a professional carpet cleaner. Specialized tools and solutions are needed to get the urine out at this point.