One of the things we do, when we are gone and my kids and neighbors are coming to the house to take care of the dogs is to make sure they use a different door from what we do. My husband and I usually come in through the garage, so when we are gone, everyone uses the front door, so the dogs are not constantly getting excited thinking that we are home and then being dissappointed. Another thing you can do is make sure the dogs look forward to the other person coming over. Maybe they have special treats they really like. Have the other person give them small pieces of treats each time they come so the dogs associate their arrival with good things, just like they look forward to you. Try to keep their routines the same. i.e., putting out their food in the same way, having them wait to follow the person out or vice versa, however you do it, keeping the same light on at night that you do, leaving a TV or radio on if you do, feeding before they go outside, if you do, wiping front feet first before back if you do. Anything that you can keep consistent is good and gives them a sense of security. The more things that change, the more their sense of confusion will grow. Just my 2 cents worth. And remember, dogs are like children, 9 days are a very short period of time overall.
Kathy