A new breed of agent is being trained to sniff out potential terrorists.

Dogs are learning to help out with homeland security at the Canine Training Center for the U.S. Customs Service (search), which is located in a rural Virginia town.

"We're looking for concealed humans or potential terrorists coming across the border," said Lee Titus, the director of the Canine Enforcement Program (search). Titus said that the school was adapting its traditional mission of narcotic detection to add elements of human detection.

The canines trained may be top dogs, but their school is not elitist; recruits come from a wide variety of backgrounds, including animal shelters. The only requirement is that the students have spirit and endurance for what can be fast and furious training, which is as much for the officers as it is for the dogs.

"It's certainly for the dog," Titus said of the training. "They're green dogs, that is untrained dogs. For the officers though, it gives them the opportunity to work with the dog and know everything about that dog. And work together as a team."

During training, the dogs that find a potential terrorist in a container are not given a doggie treat as a reward — they receive rather a rolled-up white towel.

"Its pliable and it's affordable," said instructor Michael Litwin. "And it's very absorbent too. So we can place the odor or whatever we want the dogs to find inside the towel."

Dogs that make the grade and graduate end up working full 8-hour days at airports, seaports and border crossings, and have been successful at sniffing out potential terrorists. Over 450 canine units are in service across the U.S.

"They're finding them inside of containers and railways," said Litwin. "Wherever people are hiding, the dogs will find them."

Click in the box near the top of the story to watch a report by FOX News' Catherine Herridge.