My dog attacks other dogs that she sees when we are on walks. What can I do?

My three and a half year old German Shepherd spayed bitch has a problem with charging other dogs. She is fairly well trained and comes to call immediately if I call her as soon as I see another dog. But if I am not quick enough she completely focuses on the dog and charges, if the other dog does nothing she will do nothing when she gets there. If the other dog starts to run or is an excitable bouncy type of dog she has to stop it and will chase it and grab it to pull it down and then she does no more unless the other dog does not take too kindly to this and starts a fight but she will only fight back as a last resort. She is not aggressive and is an excellent pet and friendly with everyone but she cannot handle excitable bouncy dogs and has to stop them and understandably most owners think that she is going to attack their dog. I now keep her on leash at all times as her behavior is not acceptable and I do not know how to correct it. Do you have any suggestions? I am wary about using an electric collar because we have an electric fence in our garden and Heidi is terrified of it and will not go outside when she is wearing the collar and she is also scared of anything that bleeps and resembles the warning bleep of the electric fence.



Many thanks,
Karen