Just send somebody out to shot the damn things. Really isn't that complicated. If you allow packs of feral dogs to grow out of control you really have to expect this sort of thing. I would guess that a lot of the dogs are ones "freed" by their owners who think it is more humane to abandon a domestic animal they don't want into the "wild" then it is to drop them off at a kill shelter. Makes them feel better about at least I suppose and that is all that really matters.