Removing cat urine is one of the more challenging cleaning tasks. Not only is it very pungent, the urine actually bonds with fibers in your rug. The biggest mistake when cleaning the cat urine is to not use proper cleaners.
Not only do amino acids bind with the carpet, so do salts. Salts cause a bond with an ionic charge that is increasingly difficult to dissolve the longer the urine has been on the carpet. Steam cleaning, or home made cleaners will not dissolve these strong bonds, actually steam cleaning the carpet may make the problem worse.