Ladybirder -whatever works for your dog -some dogs are more assertive than others but whatever you do should involve you raising your voice saying'no' (all dogs should understand this word) and also MAKING the dog lie down in a submissive fashion -submissive to you, not the other dog. Holding on to the dog and shouting at the other person will not work - its not the other persons fault your dog is out of control -maybe theirs is too but not your problem. You do not have to smack your dog if thats what you were insinuating. Most people are not the alpha dog in their herd as they are afraid to dicipline, thinking their dog won't 'love them' - dogs don't love , they 'respect' the leader and most are quite happy eventually to submit to thier leader.