A few weeks ago I wrecked riding a local country road when a dog ran between the wheels of my recumbent. He wasn't smart, but he was speedy! I never try to outrun a dog. The truth is that they are usually faster than me, especially if I'm on a recumbent trike. But most dogs are chasing for entertainment or herding instinct, not because they intend to be mean. At the time I was unarmed with dog deterrents, but here are my faves and things I plan to try:
1. I give a few loud "lay down!" commands. This usually works on dogs that otherwise have been moderately schooled by their owners.
2. In the past, option #2 was to squirt directly in the face with my water bottle - just water or maybe an energy drink. This nearly always works after a squirt or two
3. I will use Halt if I have it with me...which is maybe 10-20 percent of the time. I generally don't like to because, well, people are nuts for their pets nowadays and I like to avoid unpleasant confrontations. But there is a time and a place...
I saw a video recently where well-known tourist Sylvia Halpern recommended a safety whistle as being highly effective. I like this idea since I have found in the past that it also works in traffic, and on MUPs where other users have stuff blaring in their headphones. So I bought the loudest safety whistle I could find - loudest by listed specs, at least - and will try that on the next opportunity. It is a hyperwhistle, if your curious.