Our dog turned 1 last month and we had issues with separation anxiety as well -although not to the extent that you are unfortunately dealing with. I read the article below and took from it what I thought would help Hobo and began to practice. We've been working on this for about 2 months and we are seeing improvement.
http://http://www.dog-obedience-training-review.com/separation-anxiety-in-dogs.html
Good luck with Gizmo.
Rhonda