@6350630e 48" is enough to stop them. You don't need to fence in a large area to keep them out: just a small circle around the tree itself. They can't jump over it because there isn't enough room on the inside for them to fit, so they won't. The point is just to keep them from rutting on the tree, not to keep them out of an enclosed area.

That said, I've never seen a deer jump over an 8' fence. 6' sure, but not 8'. Is someone putting steroids in a deer feeder around there? 

 @394b5c0e I have no idea what's with those Michigan deer.  He said they had to put a wire roof over the garden at 8' 

Makes sense on the close perimeter.  I have a fig tree that gives us figs every other year.  So if I just put a 4' fence around it, they might not eat the figs?  We have lots of elk too.