Pepper spray is the only non-lethal thing that works on all (non-rabid) dogs. Air horns may work, but some dogs have terrible hearing. Squirting water at dogs makes some of them think you're playing (I've done it before...).

Being an owner of 2 dogs myself, I would LOVE someone to hit them with some pepper spray if they were running in the road chasing cyclists or anyone for that matter. Pepper spray is a lesson they won't forget. Dogs live longer not running in the road, so you're doing them a favor in the process.