I've had GSD's all my life. Every one of them were rescue dogs from the pound. My best was 115lb, that I had professionally trained dual personality. He was a shop dog. One morning going to the shop I see blood outside one window on the pavement, and broken glass.
When I got inside, he was there. I called the police and they deduced that he nabbed somebody, and didn't leave the shop, or returned into the shop. He wasn't cut at all.
In the rear of my bays at this one location, I had made swing out gates 6' high with wire mesh, and wood framed.The last bay was where the dumpster was kept outside. The city would back their truck up and pick up the dumpster and unload it. My dog didn't like big trucks, and especially one of the guys that would flick rocks at the gate to antagonize him.
Well, he had enough one day and got a good run at the gate, hit it with both paws, and took the gate down to the ground. He stopped for a split second until he realized he could get out. That split second also made the guy outside aware that his time was up.
The guy jumped up on the truck and the dog jumped up and bit into the guy's knee high boots, and bit into his leg to the bone. The dog wouldn't let go, and was hanging off this guys leg thrashing back and forth. I called the dog out, and the guy had to go to the hospital.
Yes, the guy tried to sue me, and wanted the dog put down as dangerous. All the police in that district knew the dog, because he was trained where their K9's were trained. After the police took statements from me and my employees, funny thing, the truck driver told the truth about the guy throwing rocks and intimidating the dog.
In lieu of dogs, and when I moved to a larger shop with more openings, I went with the accordion type gates.