I've luckily never had a run-in with a dog while riding (maybe because I mostly ride off-road), save for one time a nasty little fluffy white yapper tried to bite my ankle at a stop light as it was crossing street (it was on one of those stupid elastic/retractable leashes that clueless dog owners use).
But I do have an annoying dog next door that barks if it's outside, gets my OWN dog barking like crazy, etc. The neighbors don't care. So I bought this cheap $12 sonic dog bark deterrent:
https://www.amazon.com/dp/B079ZS78W4...roduct_details
Looked like a piece of junk but.... holy cow this thing is shockingly effective. I can't even use it if my own dog is outside, even a good distance away--it makes her totally rattled and she hides inside for an hour afterwards. To test it further, I was on a walk, and there was a guy walking two big dogs and they were barking at me, pulling, looking like they wanted to eat me, so I pointed this thing at them and man, they got totally quiet, tails between legs and tried to get as far away from me as possible. I was roughly 15-20 feet away from them. It's so small the guy couldn't see what I had in my hand--didn't register to him I'd done anything. So, I dunno, maybe I'll velcro this cheap little gadget to my bike . . .