Anti-magic
A roleplaying game topic I see regularly is the effect magic’s existence has/should have on historical architecture and, more specifically, their defenses against various threats. Namely, magic’s existence rendering those defenses irrelevant. Some essays include how game masters should rethink/redesign castles, treasure vaults, prisons, et. al.
To me, the solution is obvious: add a nullification of all magic effects to the mundane defenses of any object or location. In short, anti-magic. For this to work, anti-magic needs to be available proportionate to the level of magic in a campaign world. Thus so, historical defenses require no rethinking at all.
The simplest, most elegant solution is most likely the correct one.
Personal magical defense will may be the subject of a later post.
ADDENDUM 1: While I do see a viable market for spell-casters to specialize in creating anti-magic wards for third parties, non-casters would—rightly—be concerned about the potential conflict of interest in the hired mage. An option that does not require one mage to stop other mages would be preferable.
I recently came upon a blogpost about an example of just this option: Voidstone and Voidsteel.
ADDENDUM 2: Here is another blogpost describing a substance, Orichalcum, with anti-magic properties.
