How can I eliminate pet odor that has been in the hardwood floors for nearly two decades?

My parents have a home with hardwood floors and have let the dogs have free-range for years. They have been very lazy in regard to cleaning and the home smells like urine. I'm trying to help do a re-vamping, we are going to be putting down carpet in the home, but I don't want to put it over urine drenched floors. What is the best method for sanitizing and removing odor?