This may be my own stupidity, but I have absolutely zero fear of dogs, regardless of size or type. I always wonder if it's possible that they can sense this, because everytime a dog has started to chase me, I've been able to stop it dead in it's tracks with an angry "GET THE F OUTA HERE" or something along those lines.
That said, dogs are sprinters, so I think if you can keep it behind you for a few dozen yards, it'll **** out.