The (Sheriffs Department) Deputy who conducted the drug interdiction with their drug sniffing dog lived on my route. After observing that they stopped bringing the dog into the station, and instead took packages out to their canine unit, I stopped and asked the deputy what was going on.
He explained that the dog was "over-stimulated" inside with all the machinery, and would false alert. They had a protocol for identifying suspicious packages, and were more successful taking the packages to the dog.
It was simply a matter of establishing the most successful method of intercepting illegal drug shipments.