Would it be possible to get him into some Obedience classes (even if he's been in them before) or Flyball or Agility? He might need a job. Aside from physical excersise, they also need mental excersise. Does he like Kongs?

Could you try rehoming yourself, worst case scenario, and ask for an adoption fee to make sure he goes to a good home? I hate seeing animals go back into cages at pounds.

Best of luck to your family with Grant! If I weren't in Canada, I'd take him in a heartbeat.