I just wanted to add that when you start to practice leaving him alone, don't make a huge fuss over him when you come back into the house.
This way they do not expect attention first thing.
Just come in, take off your coat, hang up your keys and carry on with life...I usually let them all outside for a potty break while I am doing this.
When I let them back in, I do not even say hello to them.... I just go about my business and ignore them all for at least 5 minutes. does not matter what they do...I just ignore them.
Bandit, even at age 11++, always goes and grabs a bone or a stuffie (sometimes both!) and races around with it. If we paid attention to her - even if we told her 'Stop' - this behaviour it would only escalate. She runs around for a minute then goes and lays down.
We have no excitement here at all when we come and go.
Nixon barely raises his head to say "oh, gee, you're home"...they all know they will get their pats, cuddles and treats later.