It's the smart use of DISTANCE and a simple barrier. The WORST thing I can think of doing is NOT MOVING. Holy moly. Let them close the distance?? Out of what? PRIDE?? Bravado? Tueller would not agree with that, either. Let them get within striking, grappling, or stabbing distance? No freakin' way. Sorry, but I could not disagree more.
Putting the car between me and the suspected perp is also an effective test of his intent. If he proceeds to approach me AROUND the car, it's Condition Red time. An innocent beggar or person seeking directions to a destination isn't going to do that.