I would print out the ordinance for your area which states that if he dog is a nuisance to your chickens you are allowed to shoot it. On it I would write a very kind note thanking him for keeping his animals on his own property. Then I would invite him to shoot your chickens if they wander onto his property (assuming your chickens don't really go a wandering). That will give him something to think about. Slip the note under the cake which you will deliver with witnesses at a time when their whole family is home. Deliver all cheerfully.
Then I would have the survey company come out and mark the land again, and install a permanent 8' fence with hotwire and turn that baby ON 24x7!
Then I would have the survey company come out and mark the land again, and install a permanent 8' fence with hotwire and turn that baby ON 24x7!