That is somebodys pet.
We need to predator proof every inch of our coops, that way, if a dog, or cat comes into your yard, there is no way your chickens can be attacked. If a dog or cat, raccoon, etc, gets into your coop, its your fault for not predator proofing it. Its simple, predator proof your coop, or dont get mad when your chickens get killed.
That is not somebody's pet. Sure, there's an outside chance that it was fenced in, got out and the owners are frantic, however, the chances of that are slim. Most of the time, these people are allowing the dog to roam at will. I know-I live in the country where they think they are being responsible if they grab a stray and stick a collar on it. No tag, mind you, just the collar.
And although my coop is predator proof, you really cannot predator proof a fence against some powerful dog breeds, who literally tear and peel back hardware wire with their teeth to get at the birds. Sure you do your best, but sometimes, that is not enough. And really, that is irrrelevant. Because I care about my birds, my property is fenced with livestock fencing and a gated driveway, then on top of that, there are tight coops and several pens with 5', up to 7' fencing, wrapped in hardware cloth and chickenwire, which is also turned outward and buried at the base. I think by perimeter fencing this place, then providing pens on top of that, I've done as much as I should have to do. It's up to the dog owner to keep that dog on their own property. I dont care if it's the city, county or in the middle of nowhere, everyone should fence their dogs. If someone cant afford the fence to keep the dog and others safe, then that person should not have a dog, period. A pet is something cared for by the owner, enough to see to its safety. A roaming dog is not a pet, it's a predator, no if's and's or but's.
If my bird escapes my fencing and goes to my neighbor's property and is killed by their dog, I have nothing to complain about. That is why the perimeter fencing. Livestock fencing isn't that expensive, either.