"The joke around our office is that all you need for probable cause in Madison County is an Arizona, New Mexico, Texas, or Florida license plate." In the 2005 case Illinois v. Caballes, the U.S. Supreme Court ruled that having a drug dog sniff the exterior of a vehicle during a routine traffic stop does not violate the Fourth Amendment. But in a dissent to that opinion, Justice David Souter pointed to mounting evidence that drug dogs aren't as infallible as police departments often claim. Souter noted a study that the state of Illinois itself used in its briefs showing that in lab tests, drug dogs fail 12.5 to 60 percent of the time.
Update, 2 April: Lawmakers lobby Justice Department to lay off state MM industries.