“The field performance records of drug dogs are often no better—and sometimes worse —than a coin flip. Yet a dog’s alert during a traffic stop can result in a thorough search of your car, allowing police officers to snoop in all of your belongings. It can also give them cause to rip out upholstery and linings, damaging your car. (And in case you’re innocent, good luck getting compensated for it.) Worse, an alert, combined with a few hard-to-prove allegations from a cop about your body language or ‘suspicious’ answers to questions, can result in the seizure and forfeiture of any cash or valuables you happen to be carrying, even if the officer doesn’t actually find a measurable quantity of drugs.”
http://www.washingtonpost.com/news/opinions/wp/2014/01/27/a-drug-dog-named-guilty/