I loved that I could set my companion to a particular behaviour. But I forgot to turn off Woodcutting when I brought her back to my camp, and I turned my head for ONE SECOND and she'd not only cut down all my beautiful trees but also destroyed my sewing table and tanning stand! Please restrict woodcutting to "trees" and "fallen branches". (It's ok, I rebuilt them under cover and with better augments, but still)
The game actually give you the possibility to make npc not "farm".
In your case, you are asking a way to mark trees and other things that a npc will not "farm".