Indicators that provide probable cause for a search can include visible signs of other drugs, such as tools used for smoking methamphetamine like a bent, burned spoon, Calkins said.
There's disagreement among departments in Washington and Colorado whether dogs can be taught to disregard an odor once they've been drilled to hunt out the scent for years. The animals give the same alert to all drugs they're trained to find, including cocaine, methamphetamine, marijuana and heroin.
"Once you put an odor on a dog, it's very difficult to get that odor off a dog," said Fiorillo, the Colorado Springs officer. "We can't train our dogs to bark if it's cocaine, roll over if it's marijuana, scratch if it's methamphetamine."
The Seattle Police Department is no longer training its dogs to recognize the odor of marijuana, said Sgt. Sean Whitcomb, a spokesman.
"There's constant training to make sure their sniffers are up to snuff where we use real drugs from evidence and a dog is rewarded for sniffing it out," he said. "Marijuana is not something they are training on -- that skill is no longer being reinforced."
Police in Tacoma, Wash., about a half-hour drive south of Seattle, aren't doing anything differently with their drug-sniffing dogs, which are trained to detect seven different odors, including marijuana, said Officer Loretta Cool.
"There are several instances where marijuana is still illegal, if you are under 21 you cannot possess marijuana," Cool said. "If you have more than an ounce, it's illegal."
In Colorado, the Denver Police Department isn't making any changes to its K-9 program, given that marijuana is still illegal under federal law, said Sonny Jackson, a spokesman. Neither are police in the city's largest suburbs, including Aurora and Lakewood.