It is a little hard to answer from what you’ve asked, is the bark being eaten or just the leaves?  Assuming it is the leaves, I’d suggest spraying it as need when damage is seen wit Bon-Neem which is an organic pray that will kill insects on contact with pyrethrin and the the neem oil in the spray will disrupt any larvae that hatch so they can’t feed and just die.  Neem also will repel insects to a degree.  The rodents burrowing around the root system are also a problem for the tree.  I’d apply an effective rodent repellent like Mole-Max   on the soil around the base of the tree in a circular area about 5′ out from the trunk and water that in heavily.  Any rodents that are burrowing in that area will leave and leave quickly…within a few days.  Re-apply the Mole-Max if there are any signs of rodent activity in the future.   I’d also feed the tree with some organic Tree-Tone food (follow the directions on the label) right away and every spring from now on to help it recover and thrive.