I'm sorry to say that there is no quick fix that will guarantee both the dog's safety and keep him from being destructive. I'm not sure what you're looking for but if you son intends on keeping the dog, he's in for a long and difficult road.
That sounds like a really tough situation. I think it's awesome that your son rescued this dog and is trying to help him. I think there are 2 things that need to be addressed - both the immediate safety for your dog/house, but also the dog's state of mind that is causing him to act this way. A containment system would help with the first but not the second, so I think working with a veterinary behaviorist will be key in helping him actually learn to keep calm while you're away.
A friend turned her laundry room into a dog room for her SA dogs. They tiled the walls up from the floor about 5' high and removed basically everything within his reach except the appliances.
I would definitely second the suggestion of seeing a vet behaviorist ASAP. I think you'll have much better luck if you can get him on some anti-anxiety meds now. They can take some time to take effect so the sooner the better.
He sounds like a very very lucky dog to land with you.
You may need to repost your issues in the Training section for inputs, as I have to lock this Intro thread...most members do not frequent this section anyway, so you likely will get much better responses in Training.