There must be a certain smell in that area that attracted the cat to begin with. The best way to remedy the problem is to pull up that area of the carpet, paint the floor underneath to absorb the ordor and clean the carpet using the best pet stain remover you can find. There are a lot of different ones out there. I use a product put out by Hartz, but I dont know if you can find it there, but I'm sure there are alot of good products in your local pet stores. It's really important that you pull up the carpet because that odor will just return if you don't paint that area, then tack it back down again. It's a real pain, but it's cheaper than buying new carpet right?