With the start of my tour about three weeks away, I continue to stress out about the aggressive dog situation in Kentucky and Missouri. Last night I watched some YouTube videos about dealing with dogs while riding. Many of them suggest slowing down. (My reaction: AYFKM!) Often the dog will sense victory and back off. They say that you cannot outrun a dog. (This is poppycock. I’ve outrun several.) If the dog doesn’t disengage, dismount, keeping your bike between you and the dog. (This is insanity. I was out for a ride in my home town when a hyper-aggressive dog made a run for me. The dog blocked my way so I dismounted. It was a standoff for the better part of 30 minutes. Needless to say, I was terrified.) My friend Charmaine often stops and just calmly talks to the dog. It works for her somehow. A third idea is to throw small objects like roadside rocks or gravel at the dog. No need to hit the animal. Or even better you can fake like your throwing something. The dog will disengage. (This makes sense to me.)
Letter carriers use Halt or some other pepper spray product. I had a small can of Halt on a mount attached to the handlebars of Big Nellie on three bike tours in the mid 2000s. I never used it but it provided peace of mind. Halt is preferred to other products because it comes out as a stream not a mist, meaning it’s less likely to end up getting blow into your eyes. Amazingly, I found the can the other day and it still works. I can’t seem to find the mount though.
I was once attacked by a huge, aggressive dog in Belle Haven Park on the Mount Vernon Trail near my home. I was riding Big Nellie and didn’t have pepper spray. Seeing the dog’s teeth at eye level was pretty scary. I ended up going off the trail and crashing. The dog declared victory and went back to its master. I called the police. They came in minutes.
A few weeks ago, I bought a small air horn. It’s intended use is to alert bears to your presence while hiking. Yesterday I was discussing dogs with Beth at Bikes at Vienna. They don’t sell Halt but she showed me a similar, considerably larger horn that the shops sells. She also told me about a customer who rode a recumbent trike across the country and used a dog whistle of some sort. This is makes all kinds of sense to me. Since you can put it on a lanyard and hang it around your neck, it means you can have easy access without letting go of the handlebars. (My friend Reba uses a referee’s whistle instead of a bike bell.) I am riding to a local CVS to get one today.
Other options include spraying the dog with water from your water bottle or spraying the dog with bug repellent (the stuff tastes nasty). This comes out as a mist and can backfire.
As a last resort you can yell at the dog. My 2019 and 2023 biking buddy Mark simply yelled “GO HOME!” and, according to Corey his wingman, the dog would stop chasing him. Others online suggest “GET OFF THE COUCH!”.
So I plan on a multi-tiered approach. Sound first. Rock throwing second. Pepper spray third.
If you have any additional suggestions, let me know in the comments.
A Few Spokes Shy of a Wheel 
If riding with others, it’s like being chased by a bear. You don’t have to be faster than the dog.
If downhill, I go for outrunning. If flat, it depends on the angles (and is of course harder when loaded). Uphill, outrunning may not be an option.
A surprising number of dogs around here seem to have invisible fences or be amazingly well-trained. They run up to the property line but not into the road. Yelling “Go home” or “Stay” seems to be less effective than I thought it would be, but sometimes gets the dog to pause long enough to be outrunnable.
Usually I call out a friendly “Hi dog!” as soon as I hear a bark. A lot of dogs don’t run out at me, but is there a causal relationship? I don’t know.
The mail carrier in my neighborhood carries treats, not Halt.
A loud whistle or horn sounds like it could be effective. I’ve only actually been attacked once, and that was going up a mountain and the dog’s human was standing and watching. He seemed rather put out when I asked for documentation of rabies vaccination after showing him the bite. I wanted to bite him.
Like the mail carrier mentioned in the comment above, I carry treats, and drop a few in my wake as I’m riding by or away from the dog. In my experience, the dog will stop to see what I dropped, and then if they decide to resume the chase, I’ve got a pretty good head start. I ride the same routes, though, and know the dogs now and they know me, so your mileage may vary as you’re dealing with the unknown.