OP, contrary to what you say about your neighbors being good people; I respectfully disagree. No dog that is vicious should be allowed to roam. Regardless of leash law or not, the sheriff ought to be able to warn the owner of the consequences of not keeping their potentially deadly dog's actions/consequences in check.
There is a thread on TBN about a couple of dogs attacking a man on his property. He nearly lost his life. It is a horrific story, and a neighbor came to his rescue, fortunately, or he would have died. I strongly urge people to involve the authorities, at the very least to have a record of the dog's activity BEFORE something real bad could and too often does happen.
Vicious dogs don't willingly change their behavior, and certainly not without intervention on the owner's part, and that is difficult to do under the best of circumstances.
Ask yourself if one of the neighbor's actual kids was terrorizing the neighborhood, how long you'd put up with that behavior? I suspect not long.
Check out the thread I mentioned and see what can and did happen because of negligent dog owners who think it is not their responsibility to BE responsible for their dog's actions off their property. You may go to a larger caliber after reading it.