Ear protection for duck dog

Back during duck season I was watching one of the dogs in our blind when the shooting was going on. He was watching the ducks but when the guns fired he would squint his eyes the slightest bit. Now he would not flinch but you could tell the noise affected him a little. My question is why don't more duck dogs go deaf. You would think that as sensitive as a dogs ears are that all of that shooting would cause ear problems pretty early on. Most of the time the ducks were flying his ears were up so that did not give any protection. I have never thought about it until this year.