Be creative and smoke them out! 

They smoke in the house, however - I have no "proof" to prove that they do in the court of law except that I smell it and see a cloud of smoke arising from their unit every time I enter3.

Because of where Redding sits in this sort of bowl in the mountain range, smoke from even far away fires will sit on top of the town.

Make sure you have a separate entrance, windows have egress in case of fire, smoke alarms connected, parking, etc. 

. ($$$$)And make sure the smoke detectors are up (not expired) and working properly.I shudder to think how you will feel if someone burns to death in there.

Keep everything to code (smoke detectors, windows and doors, etc). 

If you do report it, let you agent know.Lastly, If there is smoke and/water damage that your policy may be paying, a Fire/Water mitigation specialist may be worth a call.  

Hey Will,As a PM in the area:-have a lawyer look over your lease-make sure EVERYTHING is in your lease (who replaces air filters, who replaces smoke detectors batteries, who cuts grass)-be thorough with background inspections-make sure tenant is aware (and is in lease) on when fines occur for late rent and how much they areThose are things that first come to mind.In can be expensive and time consuming to set it all up the first time and do it in a way that protects yourself and your investment.Let me know if I can help in any way!

Holy smokes, @Pete M.! 

You may do better but....There are some federal and state (in MA) requirements on smokes that have kicked in after a 10 year delay...so make sure u aren’t looking at 10-15k to hardwire stuff.