I've seen a rock in a stump. But I've seen far more ceramic and metal utility wiring fittings 15 feet up, by a ratio of more than 10:1 over rocks in stumps.I’m always trying different ways to mark out 16” sections. Recently I’ve been using the zip method. Where I have a zip on the left handle of the saw, and it’s cut at 16” from the bar. That seems to work pretty good.
Depending on the tree, I cut from the butt up, or sometimes from the middle and go both directions. Depends on where the tree is, or if I pull it closer to the tractor in sections or not.
When I cut down the tree I usually cut it about 20” from the ground. Then once it’s on the ground I’ll come back and cut off another chunk, leaving a short stump. I hate big stumps in the woods.
There’s a guy I know who’s convinced there are rocks in the stumps close to the ground. So he cuts all his stumps about 2’ off the ground, and then leaves them that way. I’ve been cutting stumps low for over ten years and never hit a rock. And in fact I’ve never seen a rock in a tree.
The worst is large lag bolts, with no other protruding fitting to see. Had a cut glance one of those earlier this year, which wiped out all the cutters on just one side of my chain.
If in the woods, I sometimes leave the stump. If in the yard or hedgerow, I always cut it flush, after I'm done with the rest.