I've also had bad experiences with dogs that were allowed to roam loose. In all cases the owners were the real problem, being irresponsible jerks. Still, your immediate problem is one or more dangerous animals. A Rottweiller and a German Shepherd killed my three month-old Chesapeake Bay Retriever before I could get them off of him. Being in CA I wasn't carrying, so I had to break bricks over their heads.
My dog was on a leash, by the way. The other dogs attacked without warning after we had just passed their house; no barking or growling. I found out later they had killed other small animals and obviously liked it. Their owner hadn't closed the gate; he was real apologetic at first but later tried to weasel out of paying damages. I held his feet to the fire, though.
The other time is when a pit bull had cornered my neighbor in her front yard. I was working in garage at the time so I went to help as quickly as I could with what came to hand first, a shovel handle. Other neighbors also joined in with their own garden tools and, looking a lot like the crowd that marched on Frankenstein's castle, we herded the dog back to it's house while the police responded. Not before I gave that dog a good, satisfying crack on the head when he charged my though.
When the San Diego Sheriff's Dept. finally got there I told them the next time something like this happened I was going to use my shotgun. They said it was fine with them, but I had better not miss and hit anything other than the dog.
Now that I'm in TX I'll get my CHL, and it will be something capable of dealing with large, dangerous dogs.