You can refuse a search of your vehicle. That doesn't mean the cops can hold you there for a dog to sniff it out. They can only 'hold' you there for as long as the routine traffic stop would take for whatever infraction they pulled you over for. Always remember to ask if you are under arrest, if you are being detained, and then if you are free to go.
"However, the ruling does not allow police to detain you indefinitely until dogs arrive. The legitimacy of the traffic stop still depends on its duration. Basically, if police can’t bring a dog to the scene in the time it takes to run your tags and write a ticket, the use of the dog becomes constitutionally suspect. So if you’re pulled over and police threaten to call in the dogs, you are not required to consent to searches."
Stand up for your rights!