I have used a small marine air horn for a couple of years now. Sometimes it scares the dogs, and sometimes it doesn't. Last week it startled the dog long enough for us to get by, then the dog kind of half heartedly ran after us a little ways. Sometimes it doesn't faze the dog at all. I yell too, and am always prepared to get off the bike if necessary. I would rather have it than not.

This is the one I use. You can get cheaper ones in the boating section of a big box, but this has lasted longer, comes with a velcro strap (big advantage), and you can buy refills for it, so it is worth the extra 5 bucks.

http://www.amazon.com/Falcon-Safety-...6148792&sr=1-5[URL="http://www.amazon.com/Falcon-Safety-Blast-Personal Watercraft"]