This video gives you a good view of how urine goes through carpet and in to the padding underneath. In in the urine removal video red liquid is poured into the carpet with another camera underneath to show how urine seeps into the pad. Its a good demonstration sped up so you can see it happen in real time. In the real world the urine would keep moving down ward over several hours if the urine was no cleaned up right away.
This video on urine removal illustrates why pet urine cleaners that you buy at the store fail. Those cleaners come with a trigger sprayer that doesn't allow for the cleaner to go into the carpet pad and get the urine out. Even if those cleaners did go all the way through the carpet and into the pad how would you remove it? This is why I recommend calling a professional carpet cleaner to remove urine stains in your carpet. In Tampa FL I recommend Chem-Dry of Tampa to take care of your urine stains and pet odor issues. Chem-Dry of Tampa has years of professional experience in removing urine from carpet and upholstery.
When dealing with urine in carpet and the pad it's best to call professionals with the proper tools and solutions to handle these types of issues.