On February 19th the Supreme Court unanimously ruled that police can conduct warrantless searches based on the police interpretation of a search dog. The court ruled that the dog doesn't even need formal certification.
The same is true, even in the absence of formal certification, if the dog has recently and successfully completed a training program that evaluated his proficiency in locating drugs. After all, law enforcement units have their own strong incentive to use effective training and certification programs, because only accurate drug-detection dogs enable officers to locate contraband without incurring unnecessary risks or wasting limited time and resources. - U.S. Supreme Court Feb. 9, 2013
In 2010 the University of California, Davis conducted a test of the effectiveness of drug and explosive testing dogs. Out of 144 searches of an empty room the dogs alerted 123 times - an 85% false positive result.
The courts have been watering down our Fourth Amendment rights for quite some time - almost always over the possession of a banned substance that shouldn't be illegal anyway.
- Carrol v. United States. In 1925 the Supreme Court ruled that automobiles can be searched without a warrant as long as the officer had probable cause. the search was limited to only the items the officers had probable cause to suspect. The rationale was that citizens do not have a reasonable expectation of privacy in an automobile and that because an automobile may be moved a search may be necessary to preserve evidence. The case stemmed from federal officers pulling over a vehicle they thought contained alcohol.
- Frank v. Maryland. In 1959 the Court ruled that Health Inspectors did not need a warrant to inspect a private home. This was reversed in 1967 in Camara v. San Fransisco Municipal Court.
- Terry v. Ohio. In 1968 the Court ruled that police may perform pat downs on suspects on the street if there is a reasonable suspicion that the suspect is armed and dangerous.
- Chimel v. California. In 1969 the Court ruled that police can not perform a warrantless search of an entire home when the occupant is under arrest. They can only search the area within immediate reach of the suspect.
- Chambers v. Maroney. In 1970 the Court ruled that a warrantless search may take place even if there is no reason to believe the car may be moved. In this case the police had secured the car and arrested the driver.
- New York v. Belton. In 1981 the Supreme Court ruled that the passenger compartment of an automobile may be searched without a warrant regardless of probable cause it the occupant of the automobile was under arrest.
- California v. Carney. In 1985 the Court ruled that motor homes also qualified under the Carrol automobile exception. The "element of mobility" was cited as the rationale.
- California v. Houghton. In 1999 the Court expanded the Carrol decision to include containers in the automobile regardless of ownership (e.g. a passenger's purse).
- Board of Education v. Earls. In 2002 the Court deemed mandatory drug testing of government school students as constitutional provided the students were participating in extracurricular activities in any way.
- Arizona v. Gant. In 2009 the Court reversed itself and held that police may not conduct a warrantless search a vehicle if there is no possibility of loss of evidence or danger to the officers or the public.
This is just a sampling of the many decisions that have been made by the courts. The vast majority of court decisions weakening our Fourth Amendment protections came after prohibition was enacted. Prior to 1900 there were only five cases concerning the Fourth Amendment that the Supreme Court had ruled on.