Wow. Lots of replies. I appreciate that.
I subscribe to the "broken windows" concept of crime prevention which is basically that if you allow a small problem (i.e., broken windows in abandoned businesses) to go unaddressed, the problems will worsen and eventually become out of control.
For some psychological reason unknown to me, it's a proven fact that litter encourages crime.
You guys hit the nail on the head. I don't think the problem is gangs so much as it is riff-raff. Small stuff is just now starting to attract the more serious stuff.
I talked to Dad's boss today. He says the landlord is going to "do something." Sounds to me like an empty promise. The riff-raff hang out in a treed lot next door. Boss is trying to get the county to get the vacant lot cut clean, which I think is a real possibility. Talking to him today, I think he's ready to sell the business anyway.
Selling the business? That has me thinking about buying it for the right price. Which also has me thinking harder about how to deal with the problem. If it were me, I'd get better insured for the property. And take some of the more preventative measures, to deter crime (I've gotten a lot of those from this thread), rather than focusing so much on what to do to stop a criminal who has made up his mind to victimize me.
As for moving, I don't think there really is anywhere to move where they would be safer for the same rent. Besides, these two guys aren't the type to let people like that run them off.
I suggest NO fake exterior cameras - bad legal precedents.
Personally, I'd never buy a fake camera. Real ones are so cheap nowadays, I have one on my house. But bad legal precedents? How so?