Just had a thought regarding warentless searches of cars...
The automobile search doctrine allows cars to be searched without a warrant so long as there is probable cause and the car is "readily mobile". So if a cop says he is going to search your car, or you think he is about to, and you have something illegal, just slash your tires. Now it is no longer readily mobile and any warentless search would be illegal.
@freemo
Good joke. How do you imagine getting a knife out, then get out of car, get far enough to slash your tire when cops are afraid of you to death (usually yours) and ready to shoot you if you blink wrongly?