I'm so angry and upset for you, all that hard work you've done. Stupid, stupid people!

The sad thing is even if you walked around with a huge banner some people would still ignore it, the woman with the boarder Collie needs reporting, her dog was out of control to draw blood.

This is the problem people see a dog like a GSD or cross and think their dog has a right to go into attack mode. :-(
When my youngest brothers relationship broke down I volunteered to care for his two GSD's as he worked long hours, so took up training and daily walks and at the time lived on a new housing estate even though it had plenty of fields and woodland around due to the size of the ever growing estate:rolleyes: there were lots and lots of dogs.
Now,
my dog never had a problem with aggression from any of the other dogs, but when I started to take out the GSD's I noticed a complete difference in attitude.

People and dogs became defensive.
I would often be training on the common and the GSD's are very well socialised and very laid back so no problems with them, but I would often get loose dogs charging over hackles raised, barking and growling at them, I used to get so cross with the owners and my repetive line was always,
if I had two Cav's here you would not allow your dog to do that!
some took notice, some continued daily to abuse the GSD's, who never retaliated.
In the end I am afraid I got totally fed up, with these poor dogs getting constant abuse, (have to say the worst was also a Border Collie) so I took my husbands umberella and everytime one of these dogs approached I would ask the GSD's to sit, and open up the umberella like a shield pop it infront of them and shoo the dog away, it
did work, and seemed to upset the owner enough to give us a wide berth in future, I wouldn't advise it as a training method, but you need to protect your dog and I found it worked very well, in the end you have to do something, as for
some reason people think it is ok for their dogs to attack a larger guarding breed.
If my brothers GSD's
had been got to by one of these dogs, they may well have also grown up dog aggressive, :-( you need to protect your own, you need to let rip at these people who allow it, and perhaps the umberella will work as a shield for your dog too.