I have very mixed feelings on this subject. Being the owner of 2 very large and one medium sized pitbulls I am very sensitive to this subject. What I have learned about the breed thus far in my years of experience with them is that 1. They love to dig (they are terriers) 2. They will terrorize fence lines and look aggressive i.e. barking jumping at the fence clawing at the fence 3. If their owners introduce you to them in a positive light they will look at you like a friend (unless you act aggressively towards their owners)
Now this is not rock solid in every dog, but I have rehabilitated fighting dogs and bait dogs. Pits play hard and rough (pits playing with each other can sound like an all out brawl) and love like babies (when treated properly). Typically it is not the pure breed dogs that attack, it is generally the mix breeds that people get and abuse. Any dog can be abused to its breaking point.
This is just how I would handle it, I am not you and I respect your decisions as long as you’re not actively pursuing harm to the dog (unless self defense then shoot it in the head because they will continue the attack even mortally wounded). I would give up the idea that the owners are responsible in any way. I would try to get them to introduce me to their animals and spend a little bit of quality time with them so that when they come on your property they will obey your commands. When they dig at your fence line use a firm voice with a touch of belly growl in it to show dominance. also fill in the holes on your side with chicken wire over lava rock covered with dirt and grass (dogs don’t like digging through it). If the dogs do come on your property and obey your commands, round them up with some food and call the local humane society. If they attack you will need to cull them.
Please whatever you do don’t poison them. I know it was probably said half heartedly but My boy kodi and another dog were poisoned that way, luckily I was able to save them. It is a truly horrible way to go.
Just my two sense as someone who has lived with pits and fighting dogs for many years. I hope you find a solution that keeps everyone safe.