Most country dogs are what I call "property line dogs". They know and will defend the property up to the line, and once having run off the intruder (you) will break off the chase and go home. So if you can see a fence line within sprint range, go for it.
Of course, not all dogs are property line dogs, so make sure you leave something in the tank just in case.
I'm most successful channeling my "master's voice" and in clear certain terms commanding the dog to "GO HOME!", which they do. You have to deliver this with authority, not fear because dogs can sense the difference.
I used to ride with someone who kept a rolled up newspaper in his back pocket. When a dog he'd brandish it and issue a command. Apparently folks in the country train or discipline dogs with a rolled up newspaper, and dogs recognize the authority it represents.
The one thing you don't want to do is lose control of the bike while trying to defend yourself, so find something that can end the chase, or dismount, and use the bike as a shield.
Understand that (most) dogs have no interest in biting you. They're defending the property, and will chase to run you off, or will maintain a certain distance if you stop, so it's one or the other.
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