A friend worked one summer as a relief postal carrier, was issued pepper spray for dog defense, used it, was bitten anyway. Wisdom of older, unperforated carrier: ' you gotta spray 'em before they decide to bite ya-once they've made the commitment, spray won't stop them." Friend used 5 cans of spray in the next week, spraying every visible canine. Thereafter, dogs on his route ran squalling whenever he appeared on the street. Dogs are pretty tough to discourage, and fairly tough to kill. Feral dogs were a problem in the Southern Adirondacks, due to summer visitors acquiring a pup for the vacation, and abandoning the pup upon leaving. Packs chased deer and attacked deer hunters. Deer rifles are pretty effective, but number 4 buckshotwas regarded as the best solution to packs. Alternative solution to dog aggression: get your own dog-a big dog can chase them off, a small dog can distract them while you load up. This is the "Mexican sacrificial arm knife defense" applied to dogs. Or you could get a big cat-I'm talkin' one mean pussy....