A great way to giirdle a tree is to damage the cambrium and add oil to it. Something like tree wound or paint would of been better. I think it's overpriced for what it is, but I use doc farrells heal and seal. Tree wound would of been similar. However, that doesnt look too fresh, so less worries about bugs.
Need to buy a kid a BB gun...........
Caging the tree might be a decent option.. Protect deer from rubbing, rabbits from nibbling, and maybe birds from tapping. 3ft wide 1/4" mesh would accommodate about a 12 inch trunk. Not sure if the birds would just go higher up the tree.
There's a hole in my old apple tree at home. Was pruning and training water whips last week and a little black n white woodpecker popped out. Not sure if they mess with sap, or just go for the bugs in the rot.
More for voles, but I provide premium spots for hawks and owls to perch around my orchard. One way open spot is a 4x4 with a perch and a small roof for shade and rain cover. A red tail hawk loves that. Could make a spot around mature trees more favorable, open up a 2nd or 3rd level branch so the lower one is easier to land on, if you can do it safely.
A little more open orchard space helps the predators chase things and see stuff. I went 25x25 on mostly b118 and m111's. Doing 20 ft of a row of mostly M7's this year as a trial.