Police staking out hydro store's looking for growers is equivalent to staking out pawn shops looking for stolen shit, a mosque looking for terrorist's, or a church looking for pedophiles. They shouldn't be allowed to use it to investigate people, just like they can't go by electricity usage or FLIR without a warrant.
Anyone remember how they found Michael Vick's dog fighting ring. Police used drug dogs in a dance club parking lot. The dog was walked around the parking lot and hit on a car, when the owner attempted to leave he was stopped. He had 79 grams in his trunk which was enough to get a search warrant and then they found the dogs.
I don't think that should be legal. I think there should be some kind of probable cause needed to have dogs search your car if no crimes were committed prior.
In massachusetts the police are not allowed to stop or search you based on smell alone. It's a step in the right direction. It was an easy excuse for them to bust balls when ever wanted.