Quote from @Theodore Sutton: Check out the site meetup.com and also the events page on BP for meetings up in your area to meet people like this and build relationships.

If you get cat urine in the house, it can cost you 10x the pet fee to mitigate the odor.

Usually with  a new coat of kiln and paint the odor will go away.

you can always call or email the tenant in regards to this matter. i personally smoke as well and just would want my tenants happy and not feeling accused as its a big problem with a lot of tenant v landlord situations around the country. you can always say you got a report of the odor of weed and was just verifying the smell with both tenants on the property. you can restate your conditions with smoking. you can always ask if they are legally able to do so as well (meaning medical card). depending on how you want to handle it, if you want to make it a legal warning to the tenant as well, you should write a written letter sent by mail stating you got a report of weed and this is a written warning in case this a problem down the road, you have evidence to show the court if it gets to that matter that this is not your first occurrence. best of luck!

If they were smoking outside, the odor would quickly dissipate and would not permeate the building envelope and infuse into the other units. 

The odors are not always easy to eliminate within the normal apartment turnover routine.

When a pet pees on the carpet, it's essentially toast due to the odor. 

@Theodore Welpott, they gotta be legit!  

The tenants must have a strong application and a landlord reference with the cat, pay a larger deposit and higher rent, and they are inspected more often.Nothing will stop the odor.

Even if they are spayed/neutered, cat's must use a litter box that is cleaned regularly or the odor can get bad.