Bitten a few times when I was a postie by dogs "just saying hello". It's all a big joke "dog bites postie" but some of the guys in the delivery office had some horrific scars. Learned it's no use trying to fend them off once they get too close as their fighting instinct kicks in. Staring them down certainly does not work but I've found being confident, smiling broadly and talking softly has worked with a few aggressive dogs. Failing that, the stones thing might work.
We were told to hold a bag in front of you.