Bone Plating sounds like it could be better suited as an item active

It sounds as if it would be better as an active, rather than a passive.

As a passive, the activation of it is decided by how the enemy interacts with you, rather than the other way around. This is important since the effect of the rune is so big, and something so big being tied to a passive activation with a long CD (45s) would, in my opinion, feel really frustrating to play with and against.

As an active, however, it could have intent, and its effectiveness a reflection of the individual player's skill in quick-thinking and pattern recognition. Its impact would be more consistent and anticipated as opposed to one that is seemingly random and incalculable, left up to an unintuitive scrutiny of the buff bar.