Finding dog or cat urine in the carpet is really easy using a really good UV light (or black light) and moisture probe. The UV light will tell you where the urine damage is in the carpet and the moisture probe will detect the urine salts in the carpet and the pad. Not everything is urine that the UV light detects if it is a yellow, greenish glow it is urine in the carpet. If it is a bright white it is a cleaning product in the carpet. It will also detect drink spills and all kinds of other stuff. The urine salts pulls moisture from the air into the carpet keeping it wet for months allowing for bacteria to grow and it is the bacteria that leaves the bad odor in the room. This is where the moisture probe comes in handy it detect the urine in the pad and the sub floor. If you have a dog the urine might be next to furniture leg or in the middle of the room or next to the door. If it is a cat, in most cases, it is next to the wall somewhere.
This is the UV light and the moisture probe that we use when we come out to your home. This is a High flux UV crime scene light. I am using a Dri-eaz Hydrosensr 2 to detect the urine in the pad.
Sometimes the baseboards and the drywall need to be treated or replaced, you can see this is a cat because they like to pee next to the walls and baseboards.
If you pull back the carpet, you will have a good idea on how bad the urine damage is and you might have to replace the pad and seal the sub floor. In some cases, you might need to get new carpet. This is a good example of a dog that left urine on the carpet.