Doesn't a tree grow from the top (meaning that a section at the base today will still be at/near the base in 20 years)? If so, wouldn't it be safe to assume that any "serious" metal would be in the bottom 3-5' (estimated max height of a fence post or fence wire)? Wouldn't you be able to mill the sections of the tree above say, 5 feet? There might be a stray nail here or there above 5' (someone hanging a sign, birdfeeder, etc. up high) but wouldn't that be a risk with any tree? I too, look at the cross section and think what great tabletops might have been made out of it. I realize it is too late now so I'm just curious.