I wanted to come up with protection that would not only work, but would be quick, easy, and cheap. Fencing would work, but I'd have to buy it, plus buy posts to mount it on. So I looked around for a better solution. I didn't have to look further than the pile of wood pallets. Four pallets tied together make nifty tree protectors. I could have nailed them together, but I wanted to be able to easily take them apart. So tying them was a better solution.
To date the sheep and goats have left the protected trees alone. The sheep totally ignore the trees. The goat occasionally stands up in the pallet and reaches over for a nibble. But by and by, he loses interest and moves on.
I control the worst of the weeds inside the pallet boxes by using cardboard and grass clippings as mulch. Works for me.