I happen to know someone who trained dogs to sniff out drugs, explosives and other contraband/illegal items for the federal government and military. She tells me that dogs are very effective at this type of detection. She also said that they are similar to people in that they get fatigued, are moody or can get distracted. A good handler knows when the dog simply isn't up for the task.

Using explosive detection machines as the routine detection technology is not a waste of money. Using explosive detection dogs to follow up on a package that alarmed the ETD (after ruling out other possibilities) is smart; however, it all depends on what's a reasonable time limit if the dog isn't immediately available. To say that there should be a dog at the checkpoint constantly may sound reasonable, but once again, dogs tend to get bored, distracted, moody, tired and restless.