Caleb does a good job of describing the problem with the term ‘sheepdog’ well, and even I admit that I had been swayed by Grossman’s writing on that subject. But a good look at the concept should disabuse you of the notion that you’re some sort of local hero in waiting. Go read his post & just basically copy & paste it here and that’s pretty much how I feel.
There is one further point I want to elaborate on though about this – my gut instinct is that many people claiming the sheepdog title are doing so as a shortcut. It’s like voting. So many people think they’re doing the right thing by simply ticking off a checkmark next to the right person’s name and calling it a day. Here, there are people who say “I’m a sheepdog” as if that was the strongest spell available to Hogwarts that bestows magical gifts of heroism on the utterer.
You absolutely should carry a gun if you are both physically & mentally capable. When you do, as Caleb said, it should be a mundane act. You should train when you can, keep yourself well regulated, understand the laws of your areas, and be prepared to suffer under an unjust system that loves to punish those defending their lives. The ‘sheepdog’ part of protecting society automatically happens if enough people do that and it’s not something you specifically need to be.