adults and which just want to be pets. >> the dogs are going to be exposed to higher levels of stress than your typical house dog. >> we are coming in. >> we do want them to have a certain nerves of steel if you will. >> some of the dogs go to be law enforcement dogs if it they don't make it as military working dogs. >> this k-9 responded to the newtown connecticut shooting. another dog working in law enforcement is holland. fox files met up with him and his handler, metropolitan transportation authority police officer doug joseph. this k-9 unit is helping to lead the fight against terrorism in the big apple. >> in the mta, what would he be sniffing for 12346789. >> here our primary concern is explosives on the transit system in the metro area. >> tell me how important dogs have become in the last several years to american security? >> what the dog lets us do is move around any place, any time.