Christian, like Lexi, it sounds like Marshall needs to burn energy. Also, are you giving him something to do while you're there? A chew (like a bully stick) or a toy can occupy him. Most people will tolerate a squeaking toy more than a whining dog ( esp a GSD whose whine tends to be sooo annoying...
Riley's mom brings up the idea of leashing your dog. I'm a huge fan of tethering pups (and yes, 1.5 yrs is still very much a pup.), but we have to give them something to do while they're tethered. I'll tether them to heavy furniture (the leg of the sofa is often perfect) or often, myself. I bring a rug or a blanket for them to lie on. And I give them something to occupy them.
If your pup hasn't learned "go to your rug" (which also means "and stay there") start working on that at home, your yard, office, training facility, wherever is feasible.
sort of explains "go to your rug" except that I train it with a lot more treats. I want The Rug to be a magical special place where treats and toys appear, and nothing bad ever happens. My dogs aren't told to sit, lie down or stay (which means my dog can't move from a specific position). They just have to be On The Rug. We generalize this so there is no one Ideal Rug. Any blanket, pad or rug I put down is The Rug at that time. And it's always a great place to be.
Combining tethering with The Rug is particularly helpful for furry youngsters, especially when visiting others. At first, I stay nearby to continue making the rug a great place to be (providing treats or a new toy now and then, and also specifically rewarding "good quiet" ), and to ensure no one is enticing my pup to leave his area (kids and other dogs are notorious for this), or bothering him.
After my pup gets used to this, he's used to chilling out at someone else's home. I've provided him with TONS of physical exercise before I've arrived. I take him into the house on a leash, put him on a rug and leave him there for a while. No emotional greetings from your friends and family who want to see the puppy. (Explain to them that you're trying to teach him that he's not the center of the universe.
Then, once everyone's almost forgotten he's there, I disconnect the tether, walk him around the house and/or yard on leash, and with the help of the owner, introduce him to the other dogs in the yard. They're free to play, outside where it's appropriate. At any time he gets too wild, back to his rug. It's a great place to be, not a punishment. He just needs to chill again.
Eventually, the pup learns there's one way to get freedom. That's by behaving appropriately. Some pups get there faster than others. But they do learn it. As long as we're consistent (and make our friends and family be consistent), they learn it.
You don't even have to be particularly "tough" on your pup. I think this is just a matter of setting up a structure that he's destined to succeed in: 1. exercise ahead of time; 2. a safe comfortable place to hang out in with toys and chews to occupy him 3. a few reasonable boundaries and rules.