QUOTE(Dyer13 @ Jun 27 2007, 05:08 AM)

I don't know how it works as far as airports go, but as far as POLICE goes, unless they have a warrant, they CANNOT legally search your car against your will. If they do anyway after you say no, anything they find that may be illegal will be inadmissible in court, and your case will easily be dismissed.
It's called
probable cause (wiki) where they are
legally able to search you without a warrant.
QUOTE
In United States criminal law, probable cause refers to the standard by which a police officer may make an arrest, conduct a personal or property search or obtain a warrant.
In most places the standard is that they reasonable grounds to suspect you have been involved in a known crime.
BTW: even if they
say they
smelled marijuana, it does not stand up in court. Smells are subjective, one person I know clearly thinks dirty socks smell like it... and in a closed environment like a vehicle the source of the smell can easily be misidentified. Also, under no circumstance allow them to search you on such shaky grounds without a lawyer present - you
DO have rights, including the right to have counsel present even if you have not been arrested! If they decline to provide access to counsel, they are screwed when it comes time to go to court again.