I'm a little surprised at all the talk of killing a puppy, instead of working with the owner, but that's neither here nor there. I just want to share something that's working for us, and it's already been mentioned once in this thread: hot-wire.
Electric fence is cheap and effective. Why not try it? I would agree with the "it's not your problem, your fence works for you" argument if your only option was spending a ton of money to protect YOUR birds from HIS dog. A well-maintained hot-wire can save lives.
Where we live, there is, sadly, NO leash-law. And everyone knows it. We are the only people here who keep our dogs contained on our own property. So we have to protect our animals from other peoples' animals. And from our own, since WE have six dogs, all of whom happen to love chicken, as well as chasing things. They're dogs, it's what they do. They wouldn't do it with us watching, but we can't risk it any other time, either. We also have one VERY determined fox that we've been trying to catch for a while, now, so far with no luck. We know from our gamecams that the fox is still coming to the coop every night, but because of the electric wire, he can't get in.
Our chicken yard has wires running all the way around it, at 6, 12, and 18" high, another one at 3 feet high, and another one along the top of the enclosure.
You can get a small charger--it wouldn't have to cover miles and miles of fence, after all--and scads of wire for a song...the most expensive thing would be the insulators, but you can buy those in bags of 30. Put up hot-wire along the ground all along your side of the fence, and if your neighbor's amenable to it, also on HIS side. It took every one of my dogs exactly ONE time to hit the hot-wire around the chicken yard to be so scared of it that they won't go within 10 feet of it. It made a big enough impact on our biggest dog that she won't even come when we call now, if we are standing near that fence!
You'd have to maintain the fenceline, but IMO it would be worth a try--certainly no more expensive than a shock collar, and a whole lot more reliable at delivering a deterrant. And you might just be protecting your birds from predators you haven't met yet, in the process.
Belinda