In Illinois v. Caballes, 543 U.S. 405 (2005), the U.S. Supreme Court ruled that police use of a trained drug-detecting dog during a lawful traffic stop does not constitute an unreasonable search prohibited by the Fourth Amendment. But, as Justice Souter noted in his dissent, even intelligent, well-trained dogs are not infallible. "In practical terms, the evidence is clear that the dog that alerts hundreds of times will be wrong dozens of times." Caballes, 543 U.S. at 412.
Defense attorneys litigate whether a canine "alert" constitutes probable cause for a police search by filing motions in limine challenging the reliability of the dog-sniff technique. The April 2006 issue of Champion, the journal of the National Association of Criminal Defense Lawyers, has an excellent article on ways in which defense counsel can seek to exclude evidence found following "positive" dog sniffs. Jeffrey S. Weiner & Kimberly Homan, Those Doggone Sniffs Are Often Wrong: The Fourth Amendment Has Gone To The Dogs.
The article focuses on the interaction between dog, handler, and target, especially the handler's roles as trainer and interpreter. There are numerous footnotes citing to additional resources on related topics.
Thanks to Mary Whisner at Trial Ad Notes for the tip.