This thread is so timely for me. Just last night I was driving to explore a new area that I researched and it took me through the rougher east-side of town, and I though that those neighborhoods had to be something spectacular 100 years back.
In this neighborhood just a few months ago, a friend of mine was a volunteer poll worker during the election, and he was almost stabbed (cut through his hand pretty good though) because he was the only white guy waiting for the bus in this neighborhood, and they assumed that he must be there to stop their vote from counting (as they told him). Luckily, he's a former US Army Ranger and had the guy with the knife in a heap and his other two buddies didn't want any part of that, so they scattered.
Like any martial artist, he tried to calm the situation with reassuring words and a calm demeanor, keeping his head up high, but not being threatening. It didn't matter on that particular night. The knife came a-flyin' anyhow.
It's just a plain fact: in economically depressed areas, people act differently, and expecting them to treat me the same way that someone in an upscale neighborhood would treat me is illogical. I'm not saying that you should treat people like cattle or assume that every one of them will stick you with a shiv over the wheatie you found, but you need to have respect for the different social conditions and address them appropriately.
I can be a pretty intimidating looking guy, I am a martial artist as well, and I know that the way you carry yourself in dangerous situations has everything to do with your chances of being attacked, but I think Vingamel had it right: when you get into your hunting, you tend to shut out a bit of awareness of things around you. So all sorts of ideas for hunting the area ran through my mind, including hiring "protection," but I doubt you could pay anyone enough to stand around and watch you dig holes all day.
In the end, I think that a partner is the only way to go, and preferably someone who knows the neighborhood well (and isn't very good at finding the old coins LOL).