Do you have no smoking rules for your rentals?
What about smoking marijuana when they have a medical marijuana card?
You as a landlord still have some control over your rules!
Have your tenants sign a Medical Marijuana Limited Use Addendum.
There's a great website by an AZ law firm with more information and free forms for your tenants to sign, DM me for the web address.
Also, there are 2 local Meetup.com groups you may be interested in:
Cheers to your success! ;)