Hi,
I am really getting in to this so if everyone is getting bored seeing my name on every page please tell me and I'll shut up, at least for a while!!!
Seperation anxiety is stressful for everybody involved and I really feel every dog owner should have an eye on every new dog for at least six months for signs of it. The earlier it is picked up, before it becomes a problem, the easier it is to deal with. With an established pattern of destructive behaviour the only sure cure is time, effort, commitment and patience.
Do not change your routine when leaving the house, put on your shoes and coat, whatever is normal but return in a couple of minutes, praising good conduct and TOTALLY ignoring anything not so good. So no praise if there was barking or chewing. Half an hour later repeat this for 5 minutes, then 7, 10, 15 and so on. Only go add on time away when there has been good behaviour and always be over the top in your praise. Remember to totally ignore the dog if something is amiss.
This may take some time so make sure you can keep it up before you start, I had a friend who had to drive her car around the block to convince her GSD that she had gone! She had to get a neighbour to listen in the garden every half hour!! But in two weeks the dog was calm and happy to be left, hard work but worth it.
Lastly the best distraction I have found is a small red, rubber toy called a Kong. Get a couple and fill with dog food and leave in the freezer. When you leave quietly place one on the floor and instantly the dog has something else to think about. Always remove it when you return.
Hope this helps, good luck.