Matt wrote:

Yes, I know they are trying to provide housing to their descendants
and kill off a tree that provides no food, while they are planting
acorns all around.

They are causing injury to the outer layer of wood (the new growth
ring). They are biting and digging through bark and into healthy
wood. They are not mainly removing rotting wood. The trees are
mainly healthy.

So build a squirrel house or two and mount it up in the tree. They will
probably take to it right away and solve your problem for you.

Jon