One of the neighbors is in a 2 story, they also have a little fort thing and an above ground pool. The angles work out for it to have come over the fence from any of our neighbors.
Sorry to hear about your dog, I hope it makes a full recovery. We had someone shoot 1 of our dogs with a pellet gun and didn't realize it until it was too late he died of lead poisoning.
Vet and cops. Gun shot wounds can lead to compartment syndrome along the wound path, if you have an emergency vet clinic it's worth the money to get him looked at now.
Surveillance cameras covering your yard would be a good idea. It's like closing the barn door after the horses have run away but if it happens again you'll have more insight as to where it cane from.
Have you checked your yard to see where the bullet(if its that) would have impacted when your dog was shot? If you can find that im sure it will point you in the right direction. Beautiful dog, sorry to hear of your trouble.