Fill a spray bottle with ammonia, Windex or lemon juice. You can add cayenne pepper for more effect, and/of add food color to leave a mark. make sure to set the sprayer to "mist". Carry it in your downtube bottle cage.

Next time the dogs chase, spray up a storm. Don't worry about aiming accurately, just make a cloud ahead of the dogs and let them run into it. That will end the chase, and dogs aren't that stupid and will remember and associate you and burning eyes for future reference. Some dogs are slower learners, and you might have to repeat the lesson once or twice, but ALL dogs do learn, and may chase bikes, but not you.