In order for you to better understand why you can not simply mask pet odor we’re going to explain the molecular breakdown of what is causing that horrific odor.

Fresh urine usually has little odor. The offensive pet urine odor doesn't actually begin until it starts to sit and decay. At which time, it begins to release ammonia gas. A second level of decay will follow, which releases mercaptam. This comes from the same family as skunk spray therefore emitting a horrible smell.

Natural bacteria will begin to attack the urine as it breaks down and digests the urea, sodium chloride, lipids, phosphorus, and potassium contained in the urine. When this happens it leaves behind phosphate salts, which will adhere to the underneath backing of the carpet. This salt makes it extremely difficult to clean if not impossible. These salts are what release the odor and they need heat and humidity to do this. Some animals tend to revisit the same area thus supplying the heat and humidity needed for the smell to continue. As time goes on the odor will become increasingly worse each time your pet returns to that area.  
A routine professional carpet cleaning will not remove these phosphate salts from your carpet. Special enzyme cleaners are required to do this. It's very important you make us aware of the degree of your urine problem when you schedule an appointment for this service so that we may be sure to bring the right chemicals and cleaners to get the job done correctly the first time.