I don't care much for open dogs but you bring up a good point. A semi open dog may get a young dog going. But as far as a hog knowing when a dog is coming, Im not sure about that. We have walked right up on a sleeping hog and it never knew we were there because they sleep hard. If a hog is layed up sleeping, I think that a silent dog is going to get a better jump on him. If the wind is in your favor, you can also slip up on foraging hogs because they are kinda noisy themselves. But an excited open dog can ruin a sneak attack in my opinion. Now before all of the hound guys attack me, let me also state that I know that open dogs find and catch hogs every day. This is simply my take on it.
