To keep oneself intact

Two weeks ago, a librarian where I work was pushed down to the floor by a customer. This is a guy who for the last five or so years has come to the library every day. He’s either homeless or close to it, he uses study rooms to sleep or talk on his cell phone, or he uses computers, and often gets frustrated and is impatient with how we help him.
In short, he’s got some mental health issues, and has a somewhat adversarial relationship with some of my co-workers, including the woman he pushed.
Because there had been emails and incident reports about this particular individual, the library seems to be concerned about our safety and has assigned an off duty policeman to sit by the front door, specifically to stop this man from coming into the branch, as opposed to circulating and deterring aberrant behavior which has become common. Including; swearing , viewing pornography, aggressive behavior, and finally physical assaults.
We’ve only got the police in the building for two weeks before the trial of the guy who took it one step too far, then, it’s a free for all.