This pet urine will prentrate into the subfloor or cement. There was aermodel on HGTV where they had to remove carpet, then treat the floor with something. {It was on a basement concrete floor. Search HGTV to see if you can get the formula and procedure. Best wishes. Thank goodness it is an old carpet. See if the cat has a urinary track infection. Once they start this, it may be difficult to break them of it.