Running and dogs...

[HappyAnika]

As the others said, stop, so that you are not an object to be chased. A couple of "dog language" things: Don't lean forward toward/over the dog, this is an aggressive position which could invite attach from an aggressive dog. Stand straight up tall, a dominant position (which is different than aggressive). Even more effective than yelling "NO" is to growl low and loud at the dog. Think about the noises dogs make when they are fighting, or even the little grunts an older dog makes at a puppy who is annoying it. Its a deep gutteral sound that means "NO" in dog language. If you have water, accompany the growl with a squirt, this mimicks the jaw snap that dogs do to one another, which means "back off". This will work for most dogs. To be honest if a really aggressive or trained attack dog comes at you, there may not be much you can do. And really, as the guardian of two large dogs, if one of them ran up to someone aggressively and the person kicked them, I would totally understand. Don't feel bad, it's a self preservation instinct.

[Jolt]

I haven't had any aggressive dogs chase me (except for one little terrier type once, but he wasn't very threatening) but I have had dogs run after me as I run by. That's just a normal instinct. What I've done is stop, face the dog and sternly say "go home!" and if the dog doesn't begin moving in the other direction I've actually chased it back to its yard, and this has worked every time I've done it. Then I just continue on my way. I also carry pepper spray that I am prepared to use if a dog is truly aggressive (really, it's more for aggressive PEOPLE that I carry it, but it is useful in either case). That said, I'm not sure that chasing the dog is such a good idea if it is behaving aggressively.