Better still, build a prison like Russia’s Black Dolphin prison. Locate it in the most frigid, remote place we own, and staff it with wardens and guards with instructions to run the place with the same level of strictness.
Classify it one level above Supermax, and this is where domestic terrorists and all those who fund or aid them go. Once there, they no longer have a name: Only a number. And once you go in very seldom does one get out.
Or, just drop them off in the most remote, grizzly-filled part of Alaska and invite them to walk home.