I'm so sorry to her of your dogs friend getting killed. It is so sad that you need to be on the defence everytime you walk your dog anymore.
I carry mace which is against the law in CA. I would got to jail defending my babies.
I has a friend mace a dog that attacked her dog. The mace made the dog drop to the ground crying. Her dog was not hurt bad and the dog that got maced just needed its eyes washed out. The owner was someone she knew. He said his dog is afraid of cans now.
I also use a harness to be able to swing or toss my yorkie out of harms way. In my neighborhood I'm known as the lady that will kill your dog it it is loose. (I wouldn't but love it that people think I would!!!)