Most dogs will stop chasing you with a quick squirt of water from your water botle, but if you use a hydration system (camelbak ect) this isnt always posible. If its really a problem, think about carying some pepper spray.
With the smaller dogs, i sometimes slow down, and slide my foot under the dog, and toss the dog lightly (no more then 20 feet) to the side, its quite fun

Alot of the dogs around my area are trained, and a loud "NO!" or "STOP!" will usualy stop the dog, but not always.

Anyone else have any ideas?