Here, in Missouri, it is perfectly legal to shoot dogs if they are attacking Ratites (emus/ostriches). Attacking chickens? Yes, sort of (state would prefer the ower of the chooks pursue in small claims court).
If a random, unknown dog shows up here it is simply retired from the target pool.
If I know who the owner is and it is trying to get the girls I retire the dog (otherwise I return dog to owner and let them know I've got poison and Sets out for coyotes and they'd best keep their dog at home), call the Sheriff and file a nuisance animal complaint. But the complaint specifies that the dog was attacking one of us NOT the chooks/turks. It is perfectly copacetic to put down a dog that is threatening a human and, if there are no other witnesses who's to say what happened?
But, in general, it is best to SSS (or feed the Turkey Vultures). Dog was probably hit by a car, right?
Know your local laws like the back of your hand and record all conversations wiith authorities/dog owner (if it comes to that).
The fellow in the story should be pursuing action against the dog owner because the dog's worrying the hens, from outside the fence, threw off his layers and stressed out his roos...