Have you ever caught your dog barking at nothing in the backyard?

I believe the dogs are actually always barking at something even when you think there is nothing. They have much better hearing than humans. They can hear sound frequency out of the range of our human ears. When you saw nothing or heard nothing, it didn't mean there was nothing the dogs could hear or see.

I agree when you reward them for barking, it will encouraging them barking more often. If you do not wish them to bark at "nothing", reward them is the last thing you want to do at that moment lol.