Annoyingly, there doesn't seem to be a way to have any sort of repeating area-based effect, since it automatically uses the shortest time, and anything to do with teleportation is instantaneous (or up to five rounds, but that's time-based). Thus making Dimensional Anchor, Gate, and Maze impossible to create as epic spells as they're teleportation effects without an instantaneous duration. : |
If it could use the Ward duration instead (i.e., to set up an area that things get tossed out of):
Seeds: Transport + Ward. Factors: change effect to area (20' radius), double area 8 times (upping it to about a mile). DC: 110 (miiight have miscalculated this), anything non-friendly in the area has to make a saving throw or be teleported a mile above Waterdeep, mostly because this is an amusing side effect. Mitigation: one ninth-level caster (-17), then add +20 to the save DC, leading to a spellcraft DC of 133 (also conveniently what my mental estimate for the non-insanely buffed spellcraft check this character would get on a 1).
The only other option is some ad hoc Ward adjustment