Quote Originally Posted by Greywander View Post
The idea mentioned early about using the highest stone from a mountain attuning the rod to that mountain is more in line with how fantasy typically works. It does still beg questions like what happens if the mountain gets split in two, or gets leveled, or whatever, but you can probably work those out. It is at least approaching the concept from a mythological perspective, rather than a scientific one.
The kind of things leveling mountains in fantasy settings generally have people worrying less about how their immovable rod stopped working and instead how to stop the gigantic magical disaster/world ending beast can be stopped before it does more than erase a mountain.

Nitpicking aside, I agree, if you must have it stationary relative to a specific thing, a mountain is a good place to start.