I think that would depend on the circumstances of the neighborhood. In our case, the only police covering the area is the County Sheriff. He will only commit to respond in near one day, likely tomorrow. So we agree in my neighborhood to come to the aid of a
resident in need. We have had incidents which required a special plan, like a cougar stocking people taking their daily walk. One of the watch finally shot the cat.
In Martins case, I think they had responders, however, none showed up in time to prevent the worst. In my view, Zimmerman should not have been out patrolling alone. We don't do it alone, nor should he. Zimmerman is a worse case example of why patrolling alone should be avoided, too small, which invites attack by the would be bully. Being armed does not prevent and attack that you invite by being an apparent easy mark for whoop ass. The armed inviting watch meeting the would be bully lead to the shooting. Everyone is guilty for their part in the tragedy.
I don't know Zimmerman's motives, he may have been out to do good, but his tactics were very poor, contributing to the tragedy.
Martin apparently had every right to be in the neighborhood, but he sure should have let the watch in on were he lived. I don't know what the hell made him decide to go whoop ass on the piss poor watch, but it was his finally fuck up leaving Zimmerman, the piss poor watch, to take it the final step, shoot his attacker. Well hell, would Martin attack a 200 pound guy instead of Zimmerman's 135 scrawny arse? Probably not, but then still it could happen. He sure as hell would not be likely to attack two people, but if he did, then he would receive his just reward and it would not be a tragedy.