Can anyone give me tips to avoid physical altercations at my units geared towards low-income tenants? 

I've had two gentleman threaten me in the last few months. I had to call the police earlier this week on one of them because there was no way I was getting my pressure washer back without getting punched in the face or worse. The small town rumor is that dude is the dope man and he has a laundry list of small-time drug and some more significant battery convictions already. I hate calling the police, but I think in this case it was the right move.

Anyway, both were guys with criminal records not on the lease trying to live with their "baby-mamas." When I asked them about getting on the lease, they both admitted to an unacceptable criminal record, but for various reasons believed they were entitled to stay. I never argued or got upset until the physical threats started; I just kept to the facts and the policy. The first guy left without issue after the tenants realized they were going to lose their apartment; the second is tbd.

When I get unauthorized tenants, I write a very short and simple letter stating that everyone has to be on the lease and pass a background check. If I see them or talk to them about something else, I'll mention it as well. However, if I talk to them and they don't fix it or they actively avoid me, the next month I mail and post on their door the same letter with the appropriate eviction or termination notice with the opportunity to cure the problem. If they ignore that I follow through with filing an eviction. The problems occur in the time period after the second letter, but before the eviction is filed. Most people I have to work on this with, however, merely question why it matters to me, I explain it, and its just a matter of tidying up paperwork.

I'm not sure if there is anything I can do differently or better, but maybe someone has an idea for me.