Those are some excellent pointers -- the dummy cameras and the Big Red Button are ones I hadn't thought of, and you've reminded me of another I thought of a while ago and never got around to: a nice loud bell or buzzer that'll sound when the door opens, maybe with a light wired into the circuit as well -- I am sometimes running machines in the back room, and while I try to be aware of the front door, it's hard at times.
It's a service business, not retail, so yeah, greeting people, paying attention to them, sort of goes with the territory... and 99 times out of 100 I'm happy to meet them (or at least to get their business
).
And I'm not gonna go into details, but there IS a firearm on the premises, which I sincerely hope never to need... Thanks to all who've posted their thoughts, and made it that much less likely that I will.