we used a proffessonal order and stain remover(not pet one) for carpets, it removed the sent, when we first got my german shepherd, he had diharehha from worms, and to remove the ordor and stain we used it. i also know that petsmart carry proffesional pet cleaner called GET SERIOUS! Extractor, which you put in the microwave for two minutes, then apply to your area. it extracts odors, stains, and pheromone which appartently is the certian thing attracts them to marking the spot again.
heres the site, check it out and show it to your parents.
http://getseriousproducts.com/