My Skoob and now my Lilli barks preety much too. I do the same thing by going and looking out the window or door just to see what it is he's barking at. If it's someone walking by, I usually let him bark a "few" more times and if he's still going at it after their out of site (for a few) I kind of raise my voice somewhat almost if to scold him and tell him, "THAT'S ENOUGH SKOOB!" I guess I'm lucky, that's usually all it takes. Now when he was a little younger, he'd bark at the kids at the door for my kids. It got really anoying at times so I'd just call him over to me (if that didn't work I'd pick him up) and try to distract him by rubbing his belly. Just a thought, worked for me. Good Luck!