If there's one thing that does concern me, it's gang violence...
I would like to specify that I do not condone violent acts, but we must consider them in context...
Who are you going to call when there is no chance of police protecting you?
The best answers that I've seen are the suggestion that you build a community around you, support your neighbours, have your neighbours support you.
You need to be small enough to not be noticed - but if you look small, vulnerable, and resourced, you risk attracting the wrong sort of attention. If you're sitting in one spot, you become exposed to those people who have mobility; you can't afford to make a mistake, and an attacker only has to wait.
If you do decide to take an attacker on, you really need to follow Machiavelli's advice and hit hard, fast, and without quarter. Some of the best examples come from wars - if you're in an invaded village, and kill one or two soldiers, the entire town will be hit harder...
Maybe if attackers started disappearing, without any evidence of them remaining (especially none of their weapons), that would spook others enough to leave you alone.
There is the question of the morality or ethics of the situation - what actions would a response be justified? How much is justified?
Does a father stealing food for a starving child justify hanging the man? No, I don't think so; that's an easy one to think about, but scale it up from there - a group of people come to your area, and start stealing from everyone without at least offering to give some of their labour. Where is that line?
When are you justified in taking action against someone?
That, I would love to have the wisdom to answer....
My only thought is to make sure that you and your new community have some sort of judicial process. I might have to look into becoming a Justice of the Peace, if only to begin to understand some of these problems.