Dealing with squatters

[Creig Leu]

So I am just getting started on my third flip. It is in kendallville Indiana just north of Fort Wayne indiana. When I showed up this morning to get things rolling on the demo I noticed that someone lived there all this weekend. As soon as I noticed I called the police to make sure no one was still there for me. That went smoothly and the person wasn't still there. My question is. What type of things do all of you do to keep squatters out of your properties? I have tossed around a few ideas but this being my first issue I would love some advice from the rest of you! 

Thanks in advance