I have actually had experience with this. I grew up on a farm and quite a few family members still own farms. Pay the money up front for a lawyer to send a letter notifying the Dog owners that if the dogs in future are found to be threatening, harassing or harming any livestock on the property. That the livestock owners are legally allowed to destroy the dogs. Make sure the letter states it is a final notice to comply or the dogs can/will be destroyed. They don't have a leg to stand on. It does make for angry neighbours for a bit, but they have to understand that the livestock are not just pets they are income/investment. Any retaliation needs to be recorded etc if possible and they can be charged. Our neighbours came good in the end. I know it's not a good situation, but at the end of the day a dog that harms or destroys livestock in a farming situation must be destroyed or taken from the environment where this can occur.