Colnago Super (Campy/Cinelli), 70s vintage. Recent Ultegra-rigged Kestrel Evoke. Gary Fisher Superfly 100 and hard-tail Superfly. Older Marin mtb. And a 1968 Schwinn Continental I just can't manage to drop. Also a Scattante CFR w/Ultegra triple.
When I used to commute by bike and encountered dog problems, I carried the old security chain & lock across my handlebars. The one time a very aggressive dog got within range, it sent him scurrying off. However, it had limited range and you had to be careful not to overswing into your wheels.
I now ride out in the country where uncontrolled dogs are occasionally encountered. I presently carry a 9+ oz. bear spray (that claims up to 35 ft range) as my initial defense. Having been exposed to pepper spray several times, I am very careful about using it. Really unpleasant stuff.
So what if someone else did? It's seriously stupid, whether many of us do it or none of us does it. The only reason to carry a weapon like that is to get into a very violent brawl. It's not a tool for justice.