Man's Best Terror Deterrent Still Somewhat-Reliable Dog

"It's very random," Pecoraro said. "I might hit 10 stations today and 10 different ones tomorrow."

Besides sweeps, the dogs are brought onto trains and platforms to check suspicious packages. That is how they were used in London before the bombings, though they are now routinely patrolling subways there.

In the Washington area, the dogs usually are not stationed at the top or bottom of escalators, where each passenger walks by. Some days, the dogs and their handlers walk through the dark tunnels on catwalks. They press flat against the wall when a train whizzes by. When it is time to get on escalators, the dogs look anxious. Their handlers hold up their tails so they do not get caught in the moving stair.

Andy's motivation is basic: the next meal. Once an ATF explosives dog has been trained, he is fed only after he finds an explosive. Three times a day, Andy's handler hides shell casings or explosives in a field, car, building or the woods. Andy, who wears his own police badge, has to "alert" Special Agent Sheila Fry, his handler, when he smells an explosive, by sitting down at the spot. Then she hand-feeds him. She has a small "dog slobber" towel attached to her belt next to her gun.

"We don't like to say he flunked out of seeing-eye dog school. I think of it as more of a career change," Fry said. Andy "couldn't overcome his desire to sniff, track and hunt. He's great at finding explosives."

Each handler uses a different command to order the dog to start working. For Fry, it is "Seek." Potter uses "Locate." Pecoraro's command to his dog Buddy is less subtle. "Find the bomb," he says.

At the Union Station Metro stop, riders stared as D.C. canine handler Jim Shieder patrolled with his German shepherd, Ben. Several riders stopped and asked whether they could pet him.

"It makes people think something is being done," said Shawn Dooley, 42, of North Brookfield, Mass., who was vacationing in Washington and riding the Metro with his wife and two children.

One man walked by and asked Shieder whether his dog would bite. "No, he sniffs," Shieder said.

"Can he sniff drugs?" the man asked, smiling nervously.

"No, just explosives," Shieder replied.

"Whew, that's good," said the man, who declined to give his name and walked away quickly, clutching his pocket.