Baxter is just turning 3 this Feb., and we have been leaving him out for about the past six months. When he was younger, I think he had some separation anxiety, and would try to bite the door, the window sills to get out, and peed on the floor once, so we just kept him in his house (crate) while we were gone. He wouldn't necessarily want to go in, because he knew we would leave. But we would tell him, "good boy, time to go to your house", and he would walk right in- it's his safe place, and his routine ( and he gets treats when we close the door). We actually kept this routine for about two years, because he was safe and my mom would come over around lunch time and let him out to go potty, and he seemed fine with it. But we felt bad.
Once in a while, when he got older, like 1 1/2 or 2, we would leave him out while we went to dinner, or something quick, and see how he reacted. He was nervous at first, because he knew it wasn't usual for him to be out when we weren't home, but we kept trying short little tests, and he would just sleep on the couch or our bed. So we began leaving him out during the day, but I am still reluctant to leave him all day. I put him in his crate in the a.m., and my mom comes by and lets him out to potty, and leaves him in the house the rest of the day. My boyfriend thinks he should be out all the time, but I like that he's still used to going in his house, so if we need to use it, we can, and it's not too much time on his hands to get into something. So far, he doesn't touch a thing, but boxers with too much time on their hands ........ He's very smart, and I'm afraid he could find something to get into trouble with. I know not everyone is as lucky to have someone come let their dog out everyday, so it may be an all or nothing deal for you. But I also think we have guilt over the crate, but to the dog, it's his safe place ( Baxter just sleeps - whether in "his house" or with free roam). Sorry to ramble on, but my advice would be to pay attention to what he's comfortable with, and when you feel he's ready, start off with short amounts of time to make sure he sees that you come back- it's just a new routine. And, don't make a big fuss when you leave, I make Baxter lay down on the couch (which is allowed at my house) and we walk right out the door. The more you talk to them, the more apprehensive they get that something is happening. Good luck!! -Kim
P.S. I also try to walk him every day in the a.m. so that he's exercised and tired out and that encourages him to rest, instead of being on his own with a bunch of energy to burn.