I actually do not think this is the right route here. Your dog is clearly agitated by the interaction, so introducing positive punishment (air horn) is more likely to increase your dog's agitation about oncoming dogs in the future.
Here's what I might try instead:
Teach a replacement behavior. The one that comes to mind and might work really well here is a "behind" cue. This is really easy to teach: Say the cue "behind!" and toss a small handful of cookies behind you. With practice, your dog will start associating the word with getting food behind you, making him more likely to get behind you to block oncoming dogs. You might also work on asking your dog for other behaviors (sit, lie down) while your dog is still behind you. Practice this at home and slowly increase distractions.
Ask other owners to call/leash their dogs. This is sometimes easier said than done, but IME 85% of the time the other owner is competent enough to understand that there might be some conflict.
If the dog approaches and you cannot get your dog behind you: What happens if you drop the leash? I know, I know, this sounds terrifying. But often with my leash-reactive guy who I almost always walk on leash, dropping the leash when a strange dog approaches and all else fails usually results in him being more able to greet the dog in a natural way and decrease any tension and frustration caused by the leash.
Finally: I know that sometimes EVERYTHING fails and all goes to shit. I recommend carrying spray shield for those circumstances, just so you can break up a fight if needed. This would be my last resort if everything fails and the dogs are going at it, though.
i have to deal with so many off leash dogs in the area i live and it drives me mad. i have four dogs who i believe to be angels on earth but unfortunately they don’t act that way when we’re out on walks and come upon off leash dogs. for a long time i just didn’t walk them in our neighborhood because the amount of off leash dogs i saw on every walk just made me waytoofuckingtense and that ultimately made the walks unenjoyable for me and for my dogs too. now i carry direct stop and a lil air horn in my fanny pack and it makes me feel so much more comfortable knowing i have it in case shit hits the fan. neither the direct stop nor the air horn will cause any harm to a dog (we used to use both to break up scuffles when i worked at a doggy daycare). it’s gonna sound kinda cruel saying it, but my recommendation is, next time you’re out walking your dog and this dog runs up close on y’all, use the direct stop or air horn. maybe the other dog’s parents will say something to you, but a) you’re not the one breaking the law and 2) it’s not gonna hurt their dog and d) you already told them something could happen between your dog and theirs if they don’t take precautions. you might become know as the asshole who sprayed their dog with citronella spray, but you also might be the asshole who prevents them from having to deal with a dog fight or their dog getting hit by a car.
and for those not willing to pepper spray, citronella spray. It won't be harmful, but it should surprise someone enough to deter them, depending on the situation.
I would have a backup, more painful option at the ready if you're using this. If someone's out to hurt you, weird smell isn't going to deter them for long enough. This is only to deter someone if they're wishy washy about it anyway.
I've got Petsafe Sprayshield in the cupboard right now. It has a nice locking mechanism so you're not accidentally spraying yourself all the time.
If you have lots of unfamiliar dogs off-leash, it can be good insurance for a dog fight. And you're totally within your right to use it if you have warned the owner..
edit: link
http://www.amazon.com/SprayShield-Animal-Deterrent-Spray-Belt/dp/B0002XKIV6
This is the spray recommended by the ASPCA. A lot of shelters also make their employees and volunteers carry this stuff.
Also, OP, how did your conversation with the pit bull owner go? Do he/she make it seem like they wouldn't let it happen again? If it does you should contact a local pitbull rescue organization about taking the dog off of the owners hands and putting it in a safe place for training.
> A spray bottle with citronella spray works well. Avoid mace - it can cause long term problems with dogs eyesight and (from a legal viewpoint) can be considered excessive (even in dog attacks). Get a spray bottle with an accurate spray - makes it easier to hit your target.
Here ya go. I was a dog walker for a while, and Direct Stop (that's what we call the citronella spray) is a must-have in my areas around town, or when I'm handling DINOS.
Carry direct stop. Handling by the rear can be really effective, but the dogs are liable to redirect to you (bite you).
Dogs In Need of Space had an excellent blog post on this recently.
TLDR/Link phobic:
I've had very good results with this product.
They sell sprays for exactly this. Citronella sprays, Pepper Sprays, and chemical sprays that are much more intense are sold specifically to end dog fighting. Any dog trainer, or someone who has an extremely aggressive/reactive dog should have this spray handy.