Well, they probably can't do anything if the PD did show up. $20 and a few minutes will get you a medical MJ card just about anywhere in town. PD shows up, guy says yeah, I got a card. PD says ok, moves on.
Talk to the home owners assoc. they might be able to help, but probably not much they can do either. Similar if the guy next door just wants to smoke a cigar all day, it's his town house and back area to do as he wishes within the limits of the town house assoc. rules.
Get some of the fake skunk scent at the sporting goods store, keep putting it out in the back area and see if they change their mind about being out there smoking their weed.
wish you luck. Good fences make good neighbors, except when it comes to smoke or barking dogs.