I'm a GM designing the remote fortress of an ancient-but-still-living archmage (>=20th level?). The archmage lives in society at present, and only returns to his fortress a few times per year, or as needed, via a permanent teleportation circle.
Previously, the archmage hid in this fortress for centuries to escape persecution from...well...pretty much everyone, so the fortress needs to be protected against even high-level divination magic. For this reason, I plan to line the fortress with a layer of lead and have some permanent spells like Mage's Private Sanctum, Nondetection, and similar, to prevent most/all divination magic.
At the same time, because the archmage has begun living in society again (in disguise), it makes sense that he would place some kind of alarm that would warn him, even at great distances, of intruders. Furthermore, it makes sense that he'd have a sort of permanent scrying system set up so that he alone could observe what's going on in his fortress.
(Note: The archmage's INT score is way above my own, so I figured I'd do the best I can by crowdsourcing...)
- Is there any rules-as-written avenue for the archmage to simultaneously prevent others from successfully using divination spells on his fortress but also permit divination spells of his own?
- If so, how could that be done?
- If not, what might be the closest thing to it?