Auburn University is working on training dogs to detect explosive vapors before a bomb is even placed. A professor at the University claims that the dogs can catch the sent from distances of several football fields.
The dogs are trained to follow the suspect until they stop, then the dog will sit down, acting as a silent alarm for their handler. They often use Labradors and spaniels, so that attention is not drawn to the dog in a way that shepherds and other traditional K9-Unit dogs do.
Currently these dogs are in use at airports, and Amtrak trains. Surely they will be used at large sporting events in the future.