Okay, so let's start with a level 30 wizard. Already ultra-powerful, but this is mainly a thought experiment to test out certain defenses. He has Leadership, Epic Leadership, and Legendary Commander, and with boosted Charisma from epic spells, has essentially unlimited followers. He has levels in Incantatrix, War Weaver, and IotSV. Now that his power knows few if any bounds, one of his main concerns is staying alive. And he has a plan.
He constructs a spherical stone building with no entrances, an outer layer of stone, and a hollow interior, which is filled by a Gelatinous Cube. He then sets up one of his primary defenses - he creates two teleportation circles, and places a bauble to be sent between them. Since travel between the teleportation circles is instantaneous, the bauble is essentially in two places at once. Then he creates a clone of himself. Finally, with the help of an artificer follower, he creates a Contingency setup such that if the bauble is in Teleportation Circle 1, he is True Mind Switched into the inner layer of the building (temporarily turned into a creature) and his clone is sent to another plane to live in happiness well plotting more invulnerability methods, whereas if the bauble is in Teleportation Circle 2, the clone is True Mind Switched into the inner layer, and he is sent to the alternate plane.
Since the bauble's location is not clearly defined the status of both the wizard and his clone enter into a state of quantum uncertainty - sending an enormous "screw you" to divinations everywhere. Any divination pertaining to the wizard or his clone will automatically fail, since their status is undefined. Since this process works so well, the wizard does it to his cohort, and all his followers, True mind-switching them into grains of sand inside the Gelatinous Cube(to which the process is also done).
The wizard also transports Lyres of Building into the Gelatinous Cube, to be used by followers with telekinetic abilities. Since the spherical structure is a building, the Lyres can make it permanently invulnerable. Artificer followers make the outer layer into a magic item, so that it can resist abilities restricted to nonmagical objects.
The Wizard then throws up a double-layered permanent Epic Ward, which directly blocks the Afflict, Destroy, Dispel, and Transport seeds (treating them as 10th level spells). Since the Ward is double-layered, each Ward protects the other from the Destroy and Dispel seeds. The dispel DC for these wards is boosted so high that no non-epic spells can dispel it.
So the wizard (or wizard/clone) now is the inner layer of an invulnerable building, with the outer layer blocking line of effect. He cannot be tracked by divinations, nor can he be specifically targeted, thanks the fundamental uncertainty of his status, and the same goes for his followers. The interior cannot be entered, because all space is occupied. To fight, he imbues the exterior with magical properties, or simply bludgeons opponents to death by falling on them.
So, is there any way to pierce his defenses?