Personally I am dead against gentle leaders, for a few reasons, first one being that they can do major damage to a dog's neck. I used to work with a veterinary nuerosurgeon who says his #'s on neck surgery's have increased 300% since the halti's and gentle leader's became common place. They basically cause a whiplash type injury to your dog's neck. They were never meant to be used as a correction device but they are now commonly being used as such. By correcting a dog wearing a head halter you whip his head around by the nose and that is far from a natural movement a dog would make.
If the dog is a strong puller a prong collar is the way to go, first off it's a correction the dog understands--in dog language, if he was messing around with a more dominant dog and not obeying that dog's bidding the more dominant dog would bite down, putting pressure on the dog's neck with his teeth-the prong collar simulates this action.
The key is that the collar MUST be fitted properly, it needs to be snug and fitted right up behind the ears. When you're walking with the dog every time he puts pressure on the lead, you stop, let him fall back in and then carry on. He will very soon learn 2 things, 1) if he wants to have no discomfort, he doesn't tighten the lead, the prong collar doesn't feel like anything provided the dog is not tightening the collar-therefore, it is the dog's choice whether she feels any discomfort at all-your job is to ensure she always has the option of a loose leash should she choose one. 2) She doesn't get to go anywhere unless she's walking on a nice loose lead. Dog's only do what works for them, she wants to get somewhere (even if she doesn't know where) and if everytime she starts to pull, the progress stops, she will soon figure out that if she wants to go somewhere, she better do it under your rules. Dog's only do what works for them-they're smart that way, if you make it impossible for anything to work for her unless it also works for you, it won't take her long to see your way
If you have any questions on how to fit a prong collar, feel free to pm me or ask them here (you need a medium for a golden--don't go to a large or x-tra large-I don't go bigger than medium sized prongs for the largest of dog's, I just buy extra links to fit in.)