[TNO]

"A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment [...]. Official conduct that does not 'compromise any legitimate interest of privacy' is not a search to the Fourth Amendment. We have held that any interest in possessing contraband cannot be deemed 'legitimate,' and thus, governmental conduct that only reveals the possession of contraband 'comprises no legitimate privacy interest.'" -- Justice John Paul Stevens, Illinois v. Caballes

The majority opinion seems pretty reasonable to me: http://en.wikipedia.org/wiki/Illinois_v._Caballes#Majority_o...