answer:You need to have firm pack leadership so that they do not think they have to take action. Here are some tips from the pros: ”# When walking your dog, ALWAYS, keep a loose leash. Tightening the leash sends the message that something is “wrong” and that he needs to “worry”. # If your dog is lounging towards the trigger of his frustration (i.e. another dog walking), remain calm and speak to your dog in an up-beat voice. This will make YOU relaxed and your relaxed state of mind will be noticed by your dog. Move away from the dog as quickly as you can while keeping that same tone of voice.” “An effective way of helping your dog relax in the presence of strange dogs while on a leash, can be achieved by carrying some treats that your dog really likes (not he’s everyday kibble). These could be given to him as soon as HE spots the other dog. Stop feeding your dog once the other dog is out of sight. In time your dog will start associating a dog’s approach as something desirable. A second advantage to treating your dog while on a walk is that your dog will learn to focus on you. This is a great thing because it gives your dog something to do while confronted with the proximity of another dog. Consider walking your dog when hungry and yes, the food used for this type of work should be a part of his total caloric intake!” “Use a Gentle Leader (GL) head halter when you are walking your dog OR a front clip harness such as the Sensible harness which you can buy locally or on line. The GL is a humane and efficient way of giving you more control.” For barking when on leash: “Start in a controlled environment where you have the upper hand – for instance a public park with some dog traffic. Find a distance at which your dog perceives the other dog(s) but can still easily respond to simple behaviors he does well. When he does respond, reward him with a special treat such as a ball, game of tug or high value treat. Distance helps you manage your dog’s emotional arousal – in regards to the trigger that causes the behavior you are trying to change. He can look at other dog(s) as long as he’s casual about the encounter – i.e. he can sit, do tricks, etc. Eventually with time, you can get a little closer to the other dogs. ” “Please be advised, that the use of aversive treatments such as pulling on the dog’s leash, the use of prone collars, choke collars to correct the problem will only make matters worse, you might end up with a dog that is still leash reactive and aversive to you, who punish him (by pulling on the leash) every time he sees a dog! ” Source