Yes, you are correct…an agile squirrel could jump to the tree from the deck. It needs to be at least 4 feet high (the 5 to 6 feet posted on the internet is not supported by studies). I am hesitant to cut off the lower branch (so I can raise it) since it is loaded with fruit and so far I have watched a squirrel test it, but gave up quickly. After harvest, I plan on making metal cones for most all of my jujubes (need to do a lot of pruning). I noticed the varmints already wiped out a small (8 ft) Li jujube I have in the front yard.
I just have it hanging with wire since it isn’t the final location. A nail or two shouldn’t hurt though.