If you have old urine stains, try a good enzyme remover such as Nature’s Miracle. You may need to let it soak on the stain for a while, since the stain has been there a while. Use enough to get through to the underpad of the carpet. I would let it set for about 20 minutes and then blot it up. You may need to repeat this a couple times, but it should work. I have gotten old “hidden” stains out this way, and swear by this product to remove everything from urine, vomit, blood and those nasty poop accident stains.