Karen,
That does flesh it out further. I'll do the same and then give an opinion in more detail.
I've grown up around many dogs, and have raised at least 4 myself from pups. When the last German Shepherd had to be put down for hip failure, a very common illness in purebreed gs's, I decided I wouldn't have another dog. That and I was beginning to develop allergies. But I've had many in the past. I've been around black labs, gs's, rottweilers, weinreimers, st. bernards and a good number of mutts.
And I've only been around one that acted closely to the way yours is. You either need to do someting that will stop this entirely now or it will get worse. Growing up, I spent my afterschools and summers at the family buisness, an auto repair shop. The first gs I was around was a young one that was raised from pup at home then brought there. And he acted not too different than yours. It began when he wanted something, usually, either food or to be let out. And it was focused around one person at first, my uncle. Then it began to expand into the same approach to the rest of us, nipping at clothes, circling, barking agressively. And finally it was to the point we had to lock him in a room when people were in the shop as he would do it to anyone. Then finally he really attacked my uncle one evening and bit him hard. That was the end of that. Now that was a long time ago, and I've had other dogs since with no repeat of that kind of behavior, so that was one instance, but the behavior needs to be ended now before it turns into something worse.
My advice is this, you need to avoid at all costs rewarding this behavior in any way. No matter how scary the dog may be getting. That is how the dog thinks. 'I do this and I get what I want'. In the widest sense, not that much different from young kids. The big difference is the dog takes a LOT longer to develop and will never develop much futher beyond the action=reward thing. So the tack to take is reward good beahvior and try to reinforce that every way you can, and don't let up at all when it seems to be working. You need to ingrain both what is a good action and what is a bad action very deeply before they will take.
If you need advice, ask, if I don't know, my SIL is a veterinary assistant, I'll ask her.
?? I did! I win... did anybody check out my video? it will take a few minutes to load for the person who sayed it didnt work..but OMG that penguin thing is so FUNNY! Hopefully you won't be skiing on ice...
We're only supposed to be leaving here in a few hours. 
