If you have more than one dog, sometimes you need to be able to leave one home when he or she would normally expect to go. With Reagan (and all dogs), there are certain signals that start to alert her and thus get her excited. Examples include, changing clothes, putting on sneakers, and packing treats and water. Imagine her surprise and disappointment if she sees the familiar signals and then is left behind. So I change my signals. I pack treats early and placing them on the front porch. 
Next, I put a leash outside of the back door. I might then take Riley and Reagan into the backyard to potty and then only bring Reagan back inside and into her crate. I give her a stuffed Kong and I leave through the back door, grabbing Riley from the backyard as I exit through one of our gates. Reagan does not expect me to leave through the back door so watching me walk through it does nothing to generate excitement.
Another option includes preparing to leave as I normally do and loading Riley into the van (I thought driving a giant van with only 3 greyhounds was kind of excessive. Now I am down to only one small greyhound passenger in my greyhound bus, go figure.) Okay, so Riley is loaded. I return to to the house where Reagan is showing signs of excitement (since she watched Riley leave out the front door). I mill around for a few minutes waiting for Reagan to calm down. As a reward for calming down, I take her out of the crate for a little clicker training on something stationary (holding a dumbbell, for example). After a few minutes, I return Reagan to her crate with a stuffed Kong and I leave through the front door. This departure does not generate anxiety because she sees me leave through the front door all of the time (without a dog), but the knowledge that Riley and our training things are loaded into the van have long escaped Reagan's thoughts.
A little planning can greatly reduce your dog's stress when being left home alone. Similar strategies can be employed for separation anxiety as well.
