Hornbeam attack! (or what's wrong with my tree?)

I planted two European Hornbeams last year. They are still fairly young and maybe 10 feet tall. I put one in the front yard and one in the back.

To prevent my dog from digging it up, the one in the back has a pet fence around it, maybe 3 feet tall, steel fence in a circle perhaps 4 - 5 feet in diameter. The one in the front has no protection.

I just noticed the one in the back has a big chunk taken out of the base, as if something attacked it and ripped the bark and a few more layers off the tree.

What could it be? The only dog in the yard is mine. The cats go back there, but I can’t see cats leaping over that steel fence to do that kind of damage.

That leaves some other things such as squirrels, raccoons, mice, rats, or oppossum, all of which have been seen in the general area at one point or another. It’s a 1940’s subrurban house, so it’s not going to be bears or beavers.

What could it be, and what can I do to prevent some beast from chomping down my hornbeam?

I’m also surprised that there is no damage to the unprotected hornbeam in the front yard. Perhaps the front yard is too busy next to the roadway while the back yard is more peaceful for critters of the night. I’m just surprised that any critter would hop over that fence to get at a tree trunk.

I was thinking about applying tobasco sauce or Raid bug spray until I can put some kind of protective collar on it.

The only other possiblitiy I can think of is some kind of disease. However, the thin layer of bark looks like it was ripped off, and the damage only occurs at the base of the tree. Thus, disease does not seem likely to this layman.

Maybe an aluminum foil wrap will help?