In my house, where the cat decided to use the formal living room as the backup litterbox, I tried using a Rug Doctor. (It worked fine on my bachelor apartment where the soil was mostly tracked-in dirt, cigarette ashes, and a a few spilled bongs and beers.)
The carpet now needs to be replaced.
The problem with Rug Doctors and pet urine is this: 99% of the urine goes straight thru the carpet layer, soaks into the pad, and seeps out. If, for some reason, the urine is never blotted up when still wet, then you have a dime-sized spot on the carpet, and a serving-platter sized stain from hell in the pad underneath.
Now, when you make a pass with the rug doctor what happens? Well, normally when you run the rug doctor across a point on the floor, the jets spray the spot, then the brushes agitate the carpet fiber, and then the powerful vacuum sucks up the dirty water into the tank, leaving a clean spot.
However, when you have cat piss soaked into the pad underneath, what happens? First you soak the carpet with rug doctor juice, just enough to dampen the pad and reactivate the months-old urine, now extra pungent. Then the brushes come along to guarantee extra good contact between the pad and the carpet. Finally the vacuum sucks the rug doctor juice back into the tank, drawing the urine up from the pad and leaving it in the carpet fibers.
I didn’t figure this all out until after the first time I rented a Rug Doctor and ran it across the affected parts of the carpet. It seemed to do a wonderful job at first. Then the drawn-up urine discolored the carpet within 24 hours, leaving big smelly orange streaks. So then I began to form a mental picture of what was happening, so I rented the machine again, and just used it without detergent, going over and over and over and over the stains to try and rinse out as much urine as I could. Then I made a couple of passes with detergent.
Same overall effect, in the long run.
Now I’m working up the ambition to pull up the carpet, disinfect the slab underneath and replace the pad. I’m hoping that before I replace the pad, I can lay the carpet down and get the stain out.
But I’m not counting on it.