The functions include search and rescue missions; detection of hidden aliens, narcotics, and contraband; search and tracking of criminal suspects; and public relations, notably school education programs. The dogs are "selection tested" in Belgium by a team of canine instructors to determine suitability for training. Dogs purchased by the U.S. Border Patrol are immediately sent to one of the "sniffer-dog academies." There the animals are introduced to selected agent handlers, with whom they work for 9 weeks. Upon graduation, the teams are qualified to locate narcotics and hidden illegal aliens. The teams receive weekly maintenance training and are recertified every 6 months. Dog-agent teams are together 24 hours a day on duty and at leisure. Smugglers' attempts to mask odors are futile, since dogs are capable of smelling more than one odor simultaneously. Research indicates a dog's sense of smell is approximately 6 million times greater than that of humans. In the first 9 months of fiscal year 1989, dogs in the El Paso Border Patrol Sector Canine Team sniffed out $100 million in narcotics.