SPELL_SHIELDROOM

Usage       : cast shield room
Accumulative: No
Duration    : (caster's level/2) ticks
Level       : Level 11 mage
Mana Usage  : 75

This spell envelops the room in a shimmering shield that will not allow a
mob to walk into the room. Some powerful mobs are immune to this
protection, and others will eventually break through the shield.

When used in the Wilderness, this spell requires double the usual amount
of mana.