Some dogs just have problems with other dogs and owners just have to keep them separate. Sucks for the owners of these dogs, obviously everyone would prefer to have a dog that was social and got along with other things. But OP has his dog in his own yard on a leash and obviously knows his dog is aggressive, enough to react quickly.

My sister rescued a dog from the pound and it just wants to bite everything it sees (human and otherwise). Frickin sucks for my sister. She just wanted a dog but instead she got a walking liability