No one is suggesting checkpoints or fences to keep Washington state's legal pot within its borders.
But Gov. Jay Inslee insists there are ways to prevent the bulk diversion of marijuana to the black market, including digitally tracking weed to ensure it goes from where it's grown to where it's sold.
It's not just about being a good neighbor. Inslee is trying to persuade the Justice Department not to sue to block Washington state from licensing pot growers, processors and sellers.
How well such schemes can keep pot from being diverted isn't clear.
Colorado has rules aimed at keeping its medical marijuana market in line, but police say it nevertheless reaches the black market.
