This sounds like trying to make the local grocery store upgrade their electrical system to new standards because a pedestrian claims they got hit by a car in their parking lot. It just doesn't make sense. Besides, "it could have happened like you said it did" isn't really proof of guilt in this country these days, is it? Pay an attorney to draft a letter telling the County to provide proof that the range violated the law, and that the law that was violated provides penalties that include cessation of activities. If they have any legal standing for shutting you down, such notification should be made through a court order, not from the office of the Planning Commission. Also, draft a letter letting the County know that you would be willing to grant them a construction easement so that they can upgrade the perimeter control to current standards, at no cost, if they feel it's necessary, but that they will have to work around the range operating hours, as you will continue to operate under the conditions in place when the range was built. Likewise, draft a letter to the homeowner stating that any false accusations against the range shall be addressed by suit in civil court. Drafting a couple of letters has got to be a lot cheaper than four miles of perimeter control that still wouldn't stop a bullet from being launched over it. They have a case? Make them prove it.