Detention Sphere

As per Banishment (PHB, 216) but with the following changes:

The target creature is banished within a detention sphere located in a safe, previously marked area on the material plane.

At Higher Levels. When you cast this spell using a spell slot of 6th or higher you can expend one Azorius Charm to seal the target within the sphere permenantly, ending concentration. 
If cast this way, a report must be filed with officials within 24 hours, failure to do so releases the target.