A friend was training her hunter on the roads with her long hunting whip when a German Shepard came running at them teeth barred. Owner running behind trying to call it off unsuccessfully she dropped the whip over the aggressive dogs bum a couple of time it gave up and ran back to it's owner.
She expected to be yelled at but in her eyes a) her horse was in danger b) hunting mounts are useless if scared of the hounds. The owner was incredibly apologetic said it was a new dog and got out. The owner completely understood.
Try talking to the dogs owner they may be more understanding than you think.nalso point out it can be dangerous for the dogs as well as you and your horses