How to discourage territorial barking at home

I have a 4yo intact 55 pound male Labradoodle. He has a great disposition. However he goes nuts when someone walks on the sidewalk in front of our house. The double window in our main room is only a couple of feet or so above the floor, so it is easy for him to look outside. I tried closing the blinds, but he has nearly destroyed the them and he has figured out how to "nose" the blind away from the window. I have tried calling him to me and comforting him. Sometimes that works, but his instincts usually get the better of him. What always works is when he goes to the other end of the house to track the "intruder" I put a gate up so he can't get back to the main room. He whimpers a little bit then calms right down. I have also tried spraying him with water, but I hate to do that. I don't know how to block the lower half of the window from his view.

Does anyone have any suggestions?