the only chance you would have would be to neutralise the dog's ability to smell. there is no way a trained drugs dog would miss the vast amount of odour emitted by a grow room.
The only thing that will do the job is ammonia. if the dog unwittingly takes a sniff of that stuff it will effectively put the dog out of action for a while.
the only problems you have are the placement of the ammonia, as you do not want to spike it directly at the door to the grow room, concealed or not, but on the approach to the grow room.
and secondly, you will have to explain the helpless whine the dog lets out when the ammonia hits it's mucus membrane! lol. Obviously, no permanent damage would be done to the dog, it's smell etc.. would be back to normal by the next day.