Your short answer is no. You have a right to privacy in a rented car and the police cannot search it without your consent. If you were arrested, the police can conduct what is called an inventory search, which is intended to secure any valuables within the vehicle, but the extent of the search is dictated by any search policy generated by the arresting agency. A "hit" by a dog that is properly trained to detect contraband will only provide the police with probable cause to obtain a search warrant. The police still need to obtain a search warrant before they search the vehicle.
Answered on Feb 17th, 2012 at 1:39 PM