I guess you just have to decide whether to treat it as a business problem or if it is important enough to you, be more aggressive. I'm a small SFR landlord who manages my own properties. All are local to me in two counties in Texas. When rehabbing one of my vacant properties I was a little worried about squatters. I usually went over 2 times a week or more.
While there are legal provisions for squatters to gain possession, and they vary from state to state, you certainly have a better case for possession than the squatter. Of course the cops are going to take the path of least resistance and say "it's a civil matter". Well then I guess it's also a "civil matter" when you wait until YOUR property is unoccupied and change the locks and move in. Let's see...Mr. Squatter is going to call the cops and report that you changed the locks on YOUR house and moved in yourself. When (if) they show up, are they going to arrest you (with title in hand) for burglary and breaking and entering and hand the keys to the squatter? Or will they tell him its a civil matter and go down to JP court and file an eviction claim to try to get YOU out... ;-)
I know people are saying don't do "do it yourself eviction" and they are mostly right. But the majority of the horror stories are with previously legitimate tenants that defaulted or broke terms of lease or it expired, etc. Their case for legal possession is much stronger than that of someone who just broke in.
Some of the scenarios previously suggested may have success if you are a little aggressive.
- Wait till they leave for the day to check on your vacant property and when you find that your locks are broken (i.e. your keys don't work), you hire a locksmith to change them or do it yourself.
- Gain entry to YOUR house, through whatever means, and immediately temporarily rent it with a written lease to your very large, muscular, aggressive, friend... :-) .
In Texas I have registered electronically with the Justice Courts in the counties where I have property and filing an eviction is relatively painless, even more so for squatters. Armed county constables accompany the landlord or his agent on final eviction. My guess is you could do it in about 2 weeks for less than $400 in Texas....elsewhere, I don't know.
As for confronting squatters, I am almost always armed (sometimes visibly) when I visit my properties, even though they are all in what I consider class B areas. I'm generally better armed than the local police, but this is Texas... and I have lengthy experience with firearms. The chances of being outgunned by a squatter are probably low. It's a consideration, but like any other situation I measure the risk before deciding on a course of action.
At the end of the day I'd probably recommend making the PM deal with it and then if they don't come up with a plan to prevent issues in the future, fire them. I also would aggressively pursue all civil and criminal remedies against the offenders, even if it cost extra for reasons of deterrence (and revenge...). Sure you probably won't collect, but you might feel better. :-)