Conrad,
Pepper spray works well on aggressive dogs. I know from experience that it works on 200+lb men.
My Aussie hates men in uniform ever since a young cop sprayed him. I was frikin ticked off. 200 yard private driveway, at the door, dog is barking and showing pearlie whites. Obvious the kid (criminal) he was looking for wasn't there, he sprayed anyway. He did leave a note. Mailmen drop stuff out the window knowadays.
FWIW, get OC, stay away from the cheaper maces. Think hot day, hand to hand techniques, cuffing techniques, ASP training and a conclusion of a shot accross the brow. I wish I had gills, my face would still be buried in that bucket. Worse part? Sunburned ears, yeooooooooooooooooooooooooooooooooooooooowwwwwwwwwwwwwwwww!! We don't shoot officers to demonstrate the efficiency, why do we spray em? A sniff in a bucket is bad enough. And a huge word of caution during shower time, all that water is moving south, if you get my drift. Be sane, get a tazer or Steves idea.