Fascinating to see that mate.
Some observations
That is one beautiful well trained dog you've got.
Surprising (NOT) how many small dogs behaved aggressively.
Surprising (NOT) how many owners of small aggressive dogs think it's OK to not have them on a lead..
Having always had Rotties (from when nobody even knew what they were) I always walk mine on leads in public areas. Despite what the news rags want you to believe, Rotties are normally pretty laid back, but with my first, I had an issue with one guy (a near neighbour) with a Jack Russell terrier. It would aggressively charge my 52Kg Rottie and actually bit him a couple of times while I had him on a lead. I mean this little horror would skip underneath him and try to grab his bits!
I tried the sensible advisory approach, asking the guy to make sure his dog was on a lead to prevent problems, but no go.
Eventually I lost patience and
accidentally dropped my boy's lead as the terrier attacked.
He grabbed the terrier in his jaws and shook him like a rat, and then flung him a good few yards away. The terrier's legs were going like little pistons even before he'd hit the ground and he took off like an athlete at the sound of the starting gun!
No damage, no blood, but also no more problems with the terrier. It kept a
long way away after that.