I havent encountered any dogs during my commute as it is mostly commercial areas, but the country route I ride on the weekends has a doberman that makes me extremely nervous. His house is a few hundred yards from some train tracks, uphill, and out where nobody will ever hear you scream.

I am waiting for the time that I outsprint him and then have to stop at a train. I imagine I would be toast.

Suprisingly I have more trouble with goats than dogs though. I have been chased at minimum ten times by some country goats, its all in good fun though, they are quite friendly.