Wow! Thank you all for the replies. I am pleasantly surprised that no one has criticized for me scaring the animal.
I do appreciate the opinion that I am being too patient with both the dog and its owners. My patience is driven by three things. One, I truly love animals and won't unnecessarily kill one. (That said, I won't criticize anybody who would shoot a vicious animal or a predator.) Two, the owners consider this dog to be their child. IMO, they are irrational about it. They will hate anybody who shoots this dog. If I had shot the dog on Saturday, they would have known it was me. I need their good will in the long run so I'm picking my spot very carefully. Three, the dog is protected by law until it is actually threatening me. At 75' and by the property line, they will dispute that the dog was threatening me.
I talked to the sheriff after the close encounter. He declined to talk to the owner. He made clear that I can't hunt or trap the dog. It sucks but this is the hand I have been dealt.
I have to wait until the dog is indisputably threatening me to put it down. After Saturday's events, if that dog doesn't flee my property at the sight of me, my wife, my boys or any guest, I will reasonably consider the dog to be threatening and an attack imminent (if not already in progress.) At that point, I will put the dog down.
For protection, I insist that everybody on my property carry and know how to use a loaded firearm. If they don't, they have to stay within 10' of me at all times. While the boxer/pit is the only dog that has challenged me on my property, there have been instances of large dogs roaming. Other than this one, they have all fled at the sight of a human being. My days of being amused at passive-aggressive behavior are past.
I am not legally entitled to shoot any dog running wild game in Kansas. (Any dog threatening livestock, and that includes chickens, is legal to take.) But, when hunting season comes, in addition to my bow or my 30-30, I will be caring a 22 rifle. I'll decide my action at that time realizing that the pack hunting I witnessed was amazing and scary. If I had the 22 at that point, I probably would have taken a shot. I don't blame anybody who shoots a dog or predator running game.
I agree with the comments that Ma & K are lousy, horrible neighbors when it comes to their dogs. They are irrational about their dogs. They will hate anybody that kills that dog. That is why I have let them know that a number of land owners are upset with the animal. If that boxer/pit was mine, I would put it down in a heartbeat. Other than the dogs, they are good neighbors. They stay off my property, they call me if something is amiss, they call owners of loose cattle, they keep their place mowed and very clean. But their dog ownership is a serious problem that puts others and themselves at risk. (At this point, the one-bite rule no longer protects them. They and the sheriff have been put on notice that the dog is vicious.)
I will continue to be vigilant. The dog and its owners have had enough chances. If I can legally shoot that dog, I will put it down. My family has been instructed to do the same.
I truly appreciate all the comments. I have been exceedingly patient. This is my first real land ownership and unfortunately I am learning the hard way. Thanks again.
