In 1970 the U. S. government faced a serious problem. The staff of inspectors in the U.S. Customs Service, responsible for ensuring that no dangerous or illegal materials entered the country, was on the decline. Sufficient funds were not available to increase this force. At the same time, a new flood of illegal narcotics was entering the United States, along with an increasing number of vehicles and passengers. A customs official suggested that "man's best friend," the dog, might provide the solution. Dogs can be trained to detect anything that produces an odor, including illegal narcotics. Dogs have been used ever since to detect not only narcotics but also currency, weapons, explosives, fruits, and meats.

Recently, many school districts have been using scent-trained dogs to detect drugs or other forbidden material (such as weapons) on school property, including inside students' lockers, in...