Wow- I would not have known what to do facing three dogs. About a month ago, 3 of us came up on a menacing dog on the San Gabriel River Trail. The dog was baring teeth and barking at a couple of walkers and trying to attack their dog. We stopped to let some of the chaos subside and one of walkers offered me the longish, large (about 1.5' diameter) stick he had used to keep the dog at bay. So we remounted the bikes and took off with me holding the stick out like the silliest imitation of a knight ever seen. Thankfully the dog spied another animal and ran off in another direction. I have no idea what I would have actually done with that stick had that dog stayed around.
I'm going to look into the Halt solution. We always see stray dogs on that trail.