In most cases the carpet has a protectant on it that works when the urine spot is flushed with clear warm water (NO SOAP).
But, the homeowner may have already closed that avenue, or the contaminated area may have had repeated applications of urine, which will find its way into, and beyond, the backing.
ENZ-ODOR III can be very effective IF the home owner has not applied a disinfectant to the area.
If that avenue is closed too, then approach it another way -- flush flush flush with warm water, then saturate the area with SPOTTER 601 (an acid spotter safe for wool and formulated to deal with urine).
Vacuum the area as dry as possible, flush the face fibers, then apply ODOR ELIMINATOR Fresh Sent (an encapsulant).
The idea is to first remove the source, then create an environment that bacteria cannot live in, then deodorize if necessary. Remember that products must come in contact with ALL the affected area.