There was a news story in the previous city I lived in where an elderly woman used a shotgun with birdshot (don't know the size or the range, but it looked like a modest-sized house) to defend herself against a couple of home invaders, who were later caught. The one who got shot had minor injuries, with most of the shot being stopped by his leather jacket. I guess you could say it worked, though, as both offenders fled immediately after being shot at. Personally, not something I would want to count on. If I go the shotgun route, I'd be leaning towards #1 buck, or #4 buck if I can't find #1.