This is stupid, I'm assuming you're joking.

Carry some kind of OC spray if it makes you feel safe. You'll probably never have to/get to use it, though. I've been chased before, but only ran into a problem when I was on a trail I was unfamiliar with. Flatted out after hitting a massive dip in the gravel while sprinting out of the saddle away from a massive german sheperd, thus smashing los huevos on my TT. Ran into a dead end 1/4 mile later and ended up running through a field full of thorns, thus cutting myself all the **** over. Also tripped and fell facefirst into an anthill, thus completely covering myself in ants. Like, I'm a cup of soft serve under a sprinkle-dispensing machine covered. The dog caught up to me after I gave up running, picked up a stick and decided I'd beat it to death.

Turns out he just wanted to play. I informed the owner if his dog wasn't leashed by the time I retrieved my bike, I'd be beating him to death, though.

TL ; DR, Be the alpha like johnny said. Dogs don't wanna get hurt. If you try and sprint in an unfamiliar area you can royally screw your day up like I did.