Nevada's drug dogs are trained to respond to the officers, not to the drugs. Does this surprise you? Maybe what should surprise you instead is that we ever fell for the idea that a reaction from a dog is considered a cause for reasonable suspicion.
I admire the dogs used to find bodies in the wreckage after earthquakes or tornadoes or floods, so it isn't that I think dogs are not smart enough to detect drugs. However, there is a huge difference between saving a life based on a dog's senses, and wrecking a life because a dog reacted a certain way. Kind of like polygraphs: Sure, they might be right sometimes or even many times, but the fact that they can be wrong is reason they cannot be used as evidence in court.
When dogs are used to detect drugs--high schools routinely let drug dogs find the lockers that contain drugs, for example--we are accepting the reaction of an animal as legal justification for infringing on someone's right to be free from search or seizure . The animal cannot explain its reaction, it cannot be questioned. If a cop searched a car (or a locker) with only the justification that he "had a sense" that the car/locker contained drugs, we would laugh. Why do we roll over for dogs?