I have tried multiple methods on my trees.

I have game cam pics of the deer standing on their hind legs to eat the tops off of trees in 5' tree tubes. I also have pics of them knocking down the tubes.

I have also set little barbed wire fence enclosures around my trees. It works well, but it utilizes a lot of materials AND it is a pain to climb through to weed or prune the trees.

I finally tried the patented GEHAJAKE Elevated Hoops System (as shown on some of the trees in his pic).

It works very well for the tree-deer situation on my farm. I give it two thumbs up!

(I have a $35 t-post puller from Tractor Supply that works superbly. When the trees finally grow out above the deer browsing height, it will be quite easy to remove the hoops and posts, and then re-use them on any new plantings.)