Sometimes the family pet is your floors worst enemy. Once the carpet becomes saturated, urine will seep into the backing and padding of the carpet. Often the carpet must be pulled back and treated, the pad removed and even the sub-floor treated. This can often be expensive since it requires a skilled technician to repad and relay the carpet.
If the damage is not extensive, it may be able to be soaked with special chemicals and have it extracted using whats commonly known as a water claw. Water claws hook up to the vacuum portion of a standard hot water extraction carpet cleaning machine.
Sometimes after years of exposure to urine, the carpet can become faded. This cannot be cleaned leaving the only option of re-dying the carpet.