I hadn't heard of the Halo system, so I looked it up and found:
The Halo Collar's advanced GPS/GNSS system is extremely accurate. It uses the latest geolocation technology and is more accurate than your smart phone. Halo Fences are not created using a wire, so they can't be cut, damaged, and...
I went with a friend to buy a horse. We couldn't see any horses until we got out of the car. It was then that we noticed there was no fencing and 6 horse running toward us from a dam downhill. We didn't have time to do anything but stand there in the open. Suddenly the horses dead-stopped. The...
Keep a written diary of all the dogs' destructive actions and the owners innactions regarding their behaviour. Keep your cool and don't let it get worse. Good luck.
Them being freely allowed to kill is the most reinforcement a dog can have; the behaviour will not stop now. The electric fence is the way to go for your own peace of mind. This is a horrible situation for you.