Kill target. Cast Soul Bind (PHB). Put gem in a Glove of Storing (DMG). Put glove on another willing target (let's assume these are religious assassins and they have some fanatical followers).
High-level Sorcerer/Wizard uses Teleport (not Teleport without Error) and tries for a general locale, someplace they've never been. If they're really lucky, they die, taking the original target with them. If not, they're still probably lost, since they don't know exactly where they are. Cast Imprisonment from this unknown location (don't do it at night, since you don't want to have any astronomical knowledge accidentally give it away).
Quickly Teleport (without error this time) to your secret headquarters where a high-level Bard uses Modify Memory to supplant the knowledge of where you've been with something else.
et cetera, et cetera...
The key is to layer the obfuscation so that a single Miracle/Wish won't even get you close to the original target or might even yield false information.
As someone mentioned above, deities are really the only ones who cannot be stopped by mortal magics, which just makes sense.
Greg