Anyone have experience using air horn on aggressive dogs ?

There's a whole bunch of things that MAY work on SOME dogs that are HALF-HEARTEDLY coming at you:  air horns, water bottle, coins in an aluminum can, even pepper spray and mace.  They'll stop some dogs if the dog isn't really serious.

But certain breeds of dogs, when they are SERIOUS about chasing you down and tearing into you - none of the above will work.  Not even pepper spray which won't stop some breeds.  To truly incapacitate a dog without killing it requires voltage.  Police use stun guns on people, but that's a single-shot hit or miss and wouldn't be best on a charging dog.  My advice if you're truly concerned or continually experience a dangerous dog is a police stun baton.  They come in collapsable models.  This is the recommendation of Animal Control which will carry them.  The key is that it gives you a 3-foot buffer between you and the dog.  It's also easy in that you don't have to swing it - just hold it out between you and the dog.  Make sure the dog touches it before it touches you.  Easy enough.  I used to have one in a holster on the jogging stroller when the kids were babies.

Does it work?  HALE YES!  Just raising it up is the first defense (the dog sees a club).  The second is to fire it and the sound is loud and distinctive.  Last resort - the slightest touch for a fraction of a second is enough to make even the largest dog go limp and hit the ground.  Hold the baton on the beast for 1 full second (don't need any more than that) and they'll be paralyzed for a good 5-10 minutes.

... And that's from personal experience with a pit bull mix.  (Didn't know if the owner was more terrified that their dog got loose and attacked or if they thought he was dead in the street.)

I'm not suggesting you go out and buy one and always run with it.  That's all dependent on the risk you experience with dogs.  My only point is that when the teeth are bared, the ears are back, the froth is flowing and he's running at top speed with death in his eyes...  nothing but voltage, blade, blunt trauma or firearm is going to stop him.
 

I've used it with success back when I lived in Brownsville.   After being chased regularly by dogs, I finally bought one of those air horns and kept it in my jersey pocket.  One day while out on a rural road, I saw two dogs up ahead and they clearly had an angle on me, so I knew I couldn't outrun them.  As they approached, I slowed down and blasted the horn and they both stopped dead in their tracks with a "WTF" look on their faces, which allowed me to get by.

However, a word of caution.  On another ride, I tried to do the same thing while riding at full speed, and there was a bit of a wind that day.   The horn was useless....I pushed the button and nothing but a "pfffffft" came out. 

now remember, you hold the narrow end and then turn it on...

thats a fast dog...