If they are problem dogs, and repeat offenders, I would definitely advise calling your local animal control. I've had pretty good luck doing that in those situations.

The "dismount" technique can be effective when there's only one dog, but more than one and it becomes impossible to use your bike as a shield.

Also, when there's more than one dog, pick out the "leader" and spray him first, aiming for the nose and eyes. When he stops, the others usually will too. Wait for the dog to get within range before firing, and then shoot in 1-second bursts (most pepper spray containers are only good for about 4-5 seconds of spraying).

One final word of advice on using pepper spray...be aware of wind direction! I once got a tiny bit of back spray one time on a windy day, and could feel a slight burning sensation on my lip for the next mile or two (but the dog got more than I did ).

And, before I get flamed by dog lovers...I've owned and loved dogs all my life. I'd rather spray the idiot owners than the dogs that chase, but if a dog is threatening me then he's going to get sprayed. Even if I could outrun the dog, the next cyclist to come down the road might be some little girl or a senior citizen who can't (we've had a couple of cases locally where kids have been mauled and even killed by vicious loose dogs).