Yet, it is rather easy to pinpoint a troll from the top of a tower. You just have to arrange for him to never see you: shoot when he's facing another direction, and then withdraw behind a wall element (that you eventually built if the tower is not in a good shape). Switch to stealth mode and wear the full troll set. That's it.

In the same genre; I hate when a greydwarf shaman casts his poison cloud through walls and doors. No basement is safe. It's perhaps a limitation of the Unity engine.