The first time we left our ACD Emily for a few hours, we asked our neighbor if she had barked. They told us yes. The next day we had a training day. We went through the routine of leaving, giving her a treat, & one of us drove off in the truck. The other "snuck" around waiting for her to bark, then went back in and told her "No Barking." One would leave again and we would alternate between catching her barking, and coming back in when she was not barking and praise her and give her a treat. We had to have training days the first day out each spring for a couple years, but she does not bark. She normally sits on the bench watching out the window. This method worked extremely well because Emily is so easy to train. We could have tried this with other dogs/breeds and it never would have worked...then I'd be on here asking for help.