Thanks for all the comments and I will check out those links that shade posted.
Yes, better management is in order, but I want to feel more secure in case mismanagement occurs.
I have no doubt that I could recall him if I were there. All 3 times was when I wasn't around, which unfortunately is why the events occurred.
+1 to the 4 legged lawsuit waiting to happen. The first incident was particularly scary for me since it was an elderly lady that fell down during the scuffle. Her screaming brought the entire neighborhood outside. She sprained her wrist, but lucky for me, she refused any medical attention. I visited her later in her home to express my sorrow, concern and to let her know that I would gladly take care of any of her or her dog's medical bills. Lucky for me, she was scare more than hurt. Probably only slightly more scared than I was.
I do use a pronged collar and a e-collar when I'm training him. He behaves perfectly when I'm using either. In fact, I have no doubt that in my control, no restraint is needed at all. He minds very well when he's at heal and recalls very well too.
This is literally his only bad trait. Well, that and sloppy drinking, but I can live with that.
I agree with GSDmommy's suggestion of more(controlled) interaction with other dogs. I have already started training him to stay within the gate, even when it's open. All 3 incidents happened on the sidewalk in front of our property, but outside the gate. He is already picking up on that, but I know that right now, the temptation to chase a dog would be too great for him. At least if I'm not around. I don't think he would consider it if I was around, but I haven't found anybody willing to be a Ginny Pig just yet
I'm not opposed to consulting a trainer, so it very well may come to that.
I might add that he becomes very protective of the family when he's on his leash as well. Not really overly aggressive, but definitely quick to warn people. Has anybody else experienced that?