Our girls were never raised to be aggressive and I've never encouraged them to be overtly such, though I admit that when strangers approach the house, be it the Amazon guy or an unsolicited offer to cut down a tree I egg them on a bit, asking them who the 'bad man' is. They can be a bit excitable when strangers approach the mothership uninvited...
As the girls age a bit I've noticed their getting more and more protective of mommy. This afternoon, after playing with the fam' on the Great Marsh, Plum Island and some happy-happy-funtime swimming in the Merrimack river mouth, on our way back to the vehicle, when a trio of fellows appeared headed towards us, the girls all of a sudden rushed to get in front of mommy, hackles raised with deep growls emanating from within their barrel chests. Neither of them were bluffing. They shifted their bodies so as to keep their beloved mommy between and behind them until the 'threat' had passed. One of the dudes looked particularly concerned, and as their crew snuck past us he asked, 'dayum, they ain't gonna' attack us or nuttin' is they?' I responded with, 'nah, not unless you boys give me a reason to turn 'em loose...'