I don't think the range would be a place where I be less well armed than I am when I'm at home or anywhere else.
There is an excellent example from fiction illustrating why you should always have at least one loaded weapon on your person (more are better) when you at a range practicing. If you've seen "Silverado," you should remember the scene where Emmett (Scott Glenn) is in the desert practicing and the bad guys wait until he's fired all of his guns until they make their move. Emmett had not so much as a derringer in his boot loaded.
Now, that's fiction, so some will dismiss it. Fine ...
Think of this: one of the most infamous shootouts in history was between the FBI and two guys named Platte and Mattix in Miami back in 1986. In Florida, a lot of people go out to the everglades to shoot. Platte and Mattix did exactly what the bad guys in "Silverado" did ... waiting until their victims were effectively unarmed, then robbed and killed them.
Can't happen to you? Good luck.
Situational awareness is always #1, especially when you are alone (either by yourself or among strangers). Always having the means to mount a proper defense comes right after that.
Other than matches, when I go to the range and someone is there, if I don't them I'll wait in my truck until they leave. Once I'm doing my thing on the range, I make sure I check behind myself on a regular basis and I don't let anyone I don't know approach me from behind with turning to face them.
Also,
DO NOT LEAVE ANYTHING UNATTENDED when you go downrange to check/change targets. Whether it's simple theft or if it's someone picking up your own AR, slapping a mag in it, and shooting you, it's a bad idea to leave something unattended that should always be in your control. If you're alone, take it with you when you go downrange.