Sandra is right, he does need to get out of the house. Take those dogs for a walk in the park or an easy trail. Energy begets energy and sunshine definitely has an effect on depression. Unless he's had an injury or a diagnosis like herniated disc or spinal stenosis his back pain could be tied into depression as well.

Silver had a great idea too. Ham operators are often used on large organized rides. That would give him a great feeling of being needed & useful. Plus it would tie in to something you're doing.