A followup to the OP: I located the owners and the police got their info. They were cooperative and I'll be able to get my medical and equipment bills reimbursed by their homeowner's insurance. A rotator cuff injury has surfaced since then, so I'm off the bike for a while and on light duty at work (one arm). It was a 6mo old dog, and the owner says he's not quite big enough to use the invisible fence collar. Says they were out playing fetch, he turned around and his dog was gone (after me, down a slight hill out of view). He did not see any indication that I hit the dog with the pepper spray either.

In the future my mode of operation will be to panic stop immediately, put the bike between the dog and myself while presenting defense tool of choice, re-appraise the situation and defend myself as necessary. I'm getting a little beefier longer-range pepper spray and have a paddle holster on order too.

For those saying to try a command voice, squirting water, etc... do what you want but I strongly recommend that you use the only few seconds you will get to do something decisively useful because you may only get one chance. Do the math: You spot a dog at 75 feet away, he's sprinting towards you full bore, intent and on a mission. Assuming he can sprint at 25mph, you have TWO SECONDS before you've got teeth on you or a dog in your wheels. The average person may take .5 seconds to react, leaving you 1.5s. This was pretty much what happened to me.