We have used this
and you can see from the reviews...4.5 out of 5 and 90% recommend it, that we are not alone in this view.
Most pet stores sell Natures miracle. If you have a black light use it to find the offending area. IT will glow a nice green color. The NM will remove that glow. Once gone, so is the odor.
@Anna M has a great post on this here: http://www.hometalk.com/722540/how-to-remove-urine-smell-from-carpet You can also search "pet urine" in the search bar on top of the page to find more ideas.
1 cup water and 1 cup mouthwash 1/2 cup white vinegar. Soak up with paper towels. If it still smells repeat.
Simple Solutions Urine Destroyer