At the start of a new school day last Thursday, Robinson and her drug-sniffing black Labrador retriever, Bo, were hard at work again at Richmond Community High School, looking for contraband in four classrooms picked randomly by school security officers. "There was a time, especially back in the mid-1990s, when drug use among teens was really exploding, and . . . schools were considered a safe [place] to take drugs," said Dana G. Schrad, executive director of the Virginia Association of Chiefs of Police.