We have a bad bad boy dog. In fairness to him, when we bought our house and moved in a few years ago, there had been two dogs - including a Great Dane - who apparently thought the whole house was a toilet. I am sure that whenever we left the house, our little guy went around remarking territory and got in bad habits. We replaced the carpet and pad some months in, after doing substantial renovations, but he apparently kept up the naughtiness. We had no idea until we got a black light, because he is a little 10 pounder who doesn’t dump gallons at a time, and the carpet we chose is a darker grey. But when we noticed a few yellowish spots in the hallway - from repeat visits - we got the flashlight and yikes, it looked like a crime scene someone has cleaned up but then they come in with the luminol and it lights up like a Christmas tree. So we are dealing with old stains that were never dabbed or treated immediately after the accident. I tried Nature’s Miracle and the yellow color came right back. We tried spot cleaning with a Bissell and pet stain remover and the yellow came right back. We have done whole carpet cleaning. You know what I am going to say next. So I figured why not try this, especially since all I needed to do was spray and walk away. I started in a corner area behind an upholstered chair to test color safeness. No problem there. I have attached photos where you can see the yellow in the carpet, and the clear outline of the mark in the carpet and a bit on the chair with black light (couldn’t see anything on the chair with the naked eye). After a few treatments, the carpet stain no longer has the yellow color - it has not come back light happened the other times we tried to clean so we have successfully reached and cleaned the pad. You can still see the evidence under black light. It is much much fainter but I suspect due to the age of stain and other attempts to clean, we’ll never get it black light proof. But, the bit on the chair is gone even under the black light. So after using this product, I have to join the club that says if you follow the instructions, it works! At least to remove the pee color and certainly the odor. If the stain hasn’t penetrated deeply or is fresh, like in our chair, you will probably get it out so it no longer shows under black light. It is expensive but IMO, worth it.