I have an inground fence around 1 acre. It does't keep dogs from coming in though, just my dogs from going out. Last week when my Jack Russell got chewed up they were at the far edge of their boundary on the other side of a hill.
Funny, my Lab is a trained retriever. She has a very soft mouth. I told her to get a mouse the cats had tortured and was still alive thinkin' she'd crunch it with those big teeth. Nope, she picked it up and brought it to me like it was a dove or something. ROFL! Good dog, though. 
First notify law enforcement, and DNR and make formal complaints; get the report numbers to refer to later. Make sure you fully explain the viciousness, the history, any the fear for family safety that you have. This will establish a basis for the justification of what you will likely do...shoot those dogs in defense of your dogs and your family. If you shoot first, it is likely you will be made the bad guy for shooting somebody's poor little puppy dogs. (sarcasm) If the dogs turn out to be feral, make them available to law enforcement for investigation. If the law or the DNR offer to trap them, take them up on it. I know your first protective instinct is to just shoot them, but as a 30 year (retired) cop, I have seen too many good people like yourself having the tables turned on them, even when they do the right and honorable thing. This is a cautious and proper a response I could offer. Many vicious dogs have fallen to "shoot shovel, and shut up, but that's none of my business.
Document it with the authorities. Even if they don’t care, document it. Even if your local and state laws support you in fact, document it. Paper trails cut speculation out should you become the speculated.
I'm not looking to change that. I would rather get them in a live trap, see if 1 in particular has an owner, and hand them over this latest $510 vet bill. I will call the Sheriff dept and inform them of situation. If all else fails I will just keep a sharp eye out and attempt to get rid of all the armadillos, opossums, and skunks with the conibear suggestion.
Anything a dog will eat, about ANY predator would eat.
We had a mama cat come up here and we started feeding her. She was dumped. We have the same problem. We live at the very end of a private road, but there's another gated private road that crosses the T at the end of the road and people come down and drop off animals. I had to kill an injured pit bull here, had a spikey collar on. I'm sure it was a fighting dog past its prime and the injuries were severe looking cuts from dog bites.
That mama cat took up on our back porch. She started dropping kittens. In a few years we had 6. They get killed by coyotes and bobcats and even hawks and owls around here about as fast as they can multiply, now, but mama is still here. We feed 'em, but I don't do anything else for 'em. If I find one injured, I'll euthanize it, myself. A .22 bullet is about 4 cents, no biggy. They're beneficial to me, though, keep the mice population down. What ones make it past the barn cats the inside kitties (well cared for) take out.
