Of course, crating is the answer at this age, but to be able to wean the dog from the crate, we have to get the dog to focus on something satisfying but safe. Go to the butcher, and get some femur heads, or femur heads that have been split. Get a few. Put the extra in your freezer. When you leave him IN HIS CRATE, give him one of those femur bones. When you come home, TAKE IT AWAY. he only gets it when he's in his crate. Do not leave it lying about. When you are home, it should be in the freezer with the other bones. Or, if you leave frequently during the day, leave the bone in the crate, but lock the door, so he can't get into it. It's ok to change out the bones periodically, but only one at a time, and only when you are gone.
This is what my mother did when my brother and I were young, but it was toys, and it was church. We only got to play with these special toys (that lived in her purse) during church, never at any other time. That made them special. You need to make those bones "special" enough to draw and focus his attention while bored silly.