I personally have never had to shoot a dog, don't think I ever could, no matter how mean,
however my dad has, several years ago, this large dog, looked like shepherd mix of some sort showed up on my dads land, nicest dog in the world at first, would come up and lick us, wag it's tail, greet who-ever came by, just like it lived there!, but no matter what, my dad NEVER fed it, yet it stayed mostly during the day and at night, who knows, it was in good shape for about 3 weeks, until finally started getting skinnier and skinnier, and finally my dad relented, and tossed the dog a hot-dog off of the grill, which it gobbled up.
After that, for who-knows what reason, the dog started getting meaner, and meaner, it started growling, when you came out, it would bark, and run off if you got near it.
then suddenly one day out of the blue, it attacked one of my dad's friends, knocked him to the ground, and tore up his face and arms so badly that his nose has a chunk missing from it.
my dad shot the dog right on-top of his friend (he carried a hand-gun), he said the dog never cried out, just snarled like something that sounded like pure hatred.
sounds like rabies right?, the dog tested negitve.
I understand that you had to do what you did, I find that there is no room for agressive dogs, especially one who has had an owner, a truely wild/feral dog would never allow itself to be so close to humans, just like truely feral cats.