I own a GSD, he is an adolescent dog. I never allow him off lead in public parks, I hire a private secure field like every responsible owner I know. I've lost count of the stupid owners who merrily let their dogs off lead, can't recall them and tell me their dogs are friendly. Dogs are predatory animals, no matter how cute and "friendly" they may be. I just don't know how people can own a dog and not understand this. My dog is large, fast, and strong. I train him, he knows he has to listen to me, I've been training him since the day I brought him home. He's a loveable soft thing with me and especially my children, loves every one of my friends, but he is never off lead. I have actually been told I am cruel by some dog owners, that I should let him "be a dog". Always the dog owners who have put of control dogs, that run up to my dog, and chase children on bikes. And around my area, it's always the ones with the cockerpoos, doodles, frenchies, labs and retrievers. Those dogs are dangerous, badly behaved with stupid owners. The larger breeds owners tend to keep their dogs under control, because no one wants a GSD up in their face
But if your GSD is well trained he would be fine off lead surely and would not get up in someones face? With good training (recall, stop, and leave it etc) it should not be a problem. I have a working Cocker, her recall is excellent and we let her off lead and play ball in local fields, beaches and she totally ignores other people, children and animals.
I get that a GSD and a spaniel are totally different but GSD's are intelligent and highly trainable.
The dogs that attack people like this are generally untrained, unruly and owned by thugs (at least where I live they are).