Don't know if Urine Gone will work, but it should help clean up the mess. You could also try Petzyme.
The challenge you will have now is that since the cat is already spraying, he may still do it after being neutered. Spanking him won't help (and will just make him do it more), since it is a natural intact male cat behavior and he is just being a natural cat.
Here is some info on cat spraying that may be helpful.