D: [dice] x 10 minutes

You are surrounded by a field that disrupts magic and is ethereally opaque and impassable. This barrier blocks any magical effect, both entering or leaving, though a saving throw is required to successfully block spells using more than [dice] dices. A number of people equal to [dice] may be sheltered within the barrier.

It incidently blocks ethereal creatures of [dice] HD or less.

ethereal + boundary

adapted from Wonder & Wickedness