We "babysat" for a cat for a few months and this cat pooped on the carpet. So, my cat, who was 9 years old and had been litter box trained her whole life decided she would too. She still pees in the litter box tho. I have tried everything. I locked her in the bathroom to attempt to retrain her. She would poop in the box in there, but when let out would go back to the carpet. I tried the "pet no" spray for carpet. That didn't work. I bought some kind of litter additivie that was supposed to attract her to the box. That didn't work. When it isn't terribly cold, we put her on the screened in deck, with her food and litter out there. There she uses the litter box. I don't understand!! My kids are convinced there is something wrong with her, and it was just a coincidence that she started this when the other cat was there. Is there anything medical that could cause a cat to do this?