BB wrote:

* Chicken wire buried in a ring around the tree.

this is the best method that you propose. I lined my beds with CW when
I built them, and I have had nine years of relative lack of moles/voles
in the veg garden. This year I have a huge invasion, and it seems to me
that the CW is mostly gone, I don't feel it when I drive a spade into
the beds. but for a tree, nine years is perfect.

An even better method is to mix about ten glass bottles, broken into
minute pieces, into the planting hole (I used a cloth bag and
sledgehammer to get it done). The glass is too sharp for their paws,
and it will stay that way forever. You might want to also put a piece
of CW around the trunk, partially buried, to avoid rabbits girdling the
thing, until the trees have a thick bark. Both my former crabapple and
plum have been almost girdled before the final kill by deer.

I also have kiwi, grapes, currant and raspberries planted in a former
dog run, with crushed limestone which has been only partially removed
and ultimately covered with one foot of wood chips. That area, too, has
always been free of burrows.

I should mention that the broken glass works for burrowing animals. I
once mixed broken glass in the planting hole of chestnut nuts. The
squirrels, from above, patiently picked through the glass and dirt and
got the nut every time (20 nuts). Likewise, in your case, they may
decide to emerge and just girdle it (hence the CW at the base).

Of course, you will have deer coming in. Many of my chestnuts, the
crabapple, the plum, the pawpaws, the blueberry bushes, and the three
mulberries have either been killed or severely maimed by deer in
winter. The plum, crabapple, one of the elderberries and one of the
mlberries eventually got chomped to the ground and disappeared. The
persimmon, kiwis, and currants have been unaffected. Grapes, when ripe,
get ripped from the vine by deer, in the process sometimes knocking
down the trellis. This year I am going to try to defend the small trees
with multiple layers of tomato cages, made of rebar, and chicken wire.
In the end, what they really do is keep a respectful distance from the
veg garden, which has an electric fence that has put the fear of god in
them even though it is on only one day out of ten. The rest, persimmon
and currant excepted, they destroy.