> Since you don't have much in terms of rights when crossing a border I wondered why they even bother with the pretext.
To find other "bycatch" - cash to confiscate, for example, or the gun that might be forgotten after the last hunting ride, or a pack of medicine without a prescription.
In the end it's a game of probability - assume that out of 1000 cars 1% (10 cars) have something that's not an illegal drug, but still illegal. Now, police are usually banned from warrant-less searches of vehicles for a good reason, so assuming they would follow their own rules, they would possibly only search the one car of the dude with red eyes, and the other potential hits would be missed.
Now, with a "trained dog", they have the legal authority to conduct a warrant-less search - which in turn enables more insidious stuff such as racial profiling the drivers, or simply do a rough check of all cars.
"Drug dogs" are nothing more than an instrument of abuse.
