It won't scare them away, but would maybe capture a pic of them to give to law enforcement who may be able to charge them with trespassing and/or breaking into a dwelling.

Don't have too many rules, but enforce the ones you have.

Lastly, how is any of this enforceable?

Most of the towns are just looking the other way and not enforcing local ordinance.

This loophole is being widely exploited, officials said, and measures to crack down on this creative tax planning will be included in future legislation, but will be retroactively applied as of today's date."

@Jonathan Damon  I think the issue comes in with intent.. and or a perceived scheme or repeatable business practices.and I think were some get in trouble in the states that care to enforce these laws is they basically set up exactly like a real estate agent would1.

I would think anyone with knowledge of the crime should notify the postal inspector and local law enforcement right away.

I am going to have her search for specific items such as:Probates, Divorce, Code enforcement, etc.Anyone have success with this?

@Shal PatelYou should absolutely enforce the terms of the lease. 

I think it would be hard to enforce unless you enlist the help of the non-smoking tenants which them may involve you in a lot of other complaints that as a landlord really aren't your responsibility.