Most dogs are good, UNTIL they have a bad experience with another dog, and then it can be month/years before its resoled, and with some dogs never the same again.
There a knob that walks a first cross Alsation/Husky and a pit cross and it's only a matter of time before they KILL another dog. I was on the other side of a six foot fence, if it wasn't there me and me dog would of Copt it, when I shouted at there owner to get his dogs under control, the f#####g idiot said there only saying hallow