First, this isn't a stage: it's a training issue and it won't pass on its own - you have to put in the time to train proper leash walking. And second, the prong collar isn't a good idea for a puppy, period, and it's not something you can just use like that in any case. If ever you do use it, you need to have it fitted by someone who knows what they're doing, and more importantly, you need to be trained in how to use one. In the Canadian province where I live, prong collars are not illegal, but they are on the list of training tools that can lead to cruelty charges if they are not used properly. And third, the advice to ditch the retractable leash is spot on. In addition to the dangers they present, retractable leashes actually teach dogs to pull.
Having said that: I feel your pain and sympathize with you. I have severe arthritis and I know how difficult and painful it can be to walk a dog that pulls. Walks are supposed to be fun for everyone, including the human portion of the equation, but it's hard to enjoy an activity when you're being dragged around by 50 lbs or more of undisciplined adolescent dog.
In your post you don't mention training. As Nolefan said, the problems you describe are improved drastically by formal training. If you're not already enrolled in a good basic obedience class, my first suggestion would be to do so. Look for a class that teaches humans how to train dogs, and that uses positive methods. And when you start the classes, make sure you do your homework. I figure we did at least two hours of practice at home for every hour of class - and probably more for the more difficult exercises like loose-leash walking. As well as showing you how to train your dog, the classes will change your relationship with him, from one where he does basically as he likes, to one where he does what you want. This will help with the grabbing and biting, but it won't cure it. If my dog was grabbing and biting me, I wouldn't just stand there, I'd command him to lie down and would keep him down for a short while by stepping on the leash if necessary. If you just stand there like a tree, he's able to keep up the behaviour for as long as he wants without a consequence, and he only gives it up when he's had enough. If you want to signal that the behaviour is unacceptable, you need to get him to do stop the behaviour immediately, on your terms, and replace it with a behaviour that's acceptable to you. In other words, you need to be in charge, instead of letting him be in charge.
For the loose leash walking, the system that's worked for me over the years is this: fill your pockets with kibble - feed your dog his meals like this - and set off on a walk. At first, feed the kibble constantly, one piece at a time, to keep the dog by your side on a loose leash. If he pulls (tightens the leash), do a 180 degree turn, keep walking and reward him with a piece of kibble when he catches up. The first few times you might not even get out of your driveway, because your dog has developed the habit of pulling. But gradually, with this method, he'll get used to walking next to you. Once you're getting in a few paces before the 180 degree turn, you can start spacing out the kibble a bit. You should walk quickly and be very upbeat - make it into a game. Talk all the time. Make yourself more interesting than anything else in the environment. Don't ever wait for the dog. When you do the 180 turn, it should be quick, and you should keep walking at the same fast pace so he has to run to catch up. Add in some brief (20-second) training sessions by giving stopping occasionally to give a short series of commands (sit-down-sit, stand-sit-down, spin-sit-heel, etc.) and reward generously. At the end of a half-hour walk, both you and the dog should be exhausted!
Once a dog has learned to pull, it isn't a quick fix. You may have to do the kibble thing for a period of months, gradually spacing out the pieces of kibble until you're only feeding occasionally during your walk. And you have to be consistent, and never allow him to pull. But it does work. My Golden is from performance lines and is full of life and energy, but last year, when I had a total knee replacement, I was able to take him out for a half-mile walk in our neighbourhood just four weeks after the operation. I was still using a cane outdoors and wasn't very steady on my feet (to say the least), but I was 100% confident that my dog wouldn't pull or lunge or do anything that might hurt me - and I was right. He was a great walking buddy throughout my convalescence. Those early months of intensive training paid off.
As for the lunging at people, my suggestion would be to stop all greetings during walks. You have to be strict with people you meet - tell them he's in training and he can't be petted, and leave. And teach your dog a "focus" command. At home, have him look at you - I use "watch me" as my command. I start by rewarding the dog when he looks at me on his own (I use a clicker for this, so he knows exactly what is being rewarded). Then, when he starts doing it more, to get the treat, I add in the "watch me" command. It didn't take long: he quickly learned to look at me in response to the command. Once he was doing this reliably at home, I started using the command outside. These days, when I say "watch me", he will look at me even if there are squirrels to be chased, or if we meet other dogs during our walks, and so on.
These are the things that have helped me over the years. As Rion suggested earlier, one thing you could try right away, until the training starts to work, is a front-clip harness. Choose one that doesn't restrict the dog's shoulder movement. Many dogs pull less on a harness than on a collar.
Goldens are terrific dogs, but they are big, strong dogs that were bred to work, and they are difficult as adolescents. Formal training isn't an option, as it is with some breeds: with a golden, it's essential if you want a pleasant walking companion. Best of luck, and I hope things improve for you!
Ruby 13-01-2007 to 18-03-2015.
My dog of a lifetime. I'll miss you forever.