I believe off leash walks in nature are great outlets. The dogs sniff, run, investigate, and get to see the world.
I can't imagine how tight your time is working full time with a family and a young GSD. That is tough. I don't think you have to go for miles, as long as you make the time count. 20 minutes of off leash running in the woods, with fetch and some OB mixed in, twice a day, will probably help a lot.
Fetch at a ball field for 20 minutes is also great. I've measured distance and dogs have run 4 miles plus (all out) in that short time. Tug play can go a long way building a bond and giving the dog a great workout. It only takes 5-10 minutes if you do it right. Fetch at a lake is even better.
Biking can also be a nice option. He's old enough now. Buy a springer dog runner and go for a bike ride on a dirt path or dirt road. It is a great way to run the dog when you are short on time.
But some dogs are just destructive and need to be crated or contained when left alone even if well exercised. I have one of those. I think she'll improve with age, but at the moment, I need to put everything out of reach or supervise or crate. It's just how it is with some dogs- exercise or not.