Dismissal

Dismissal is an abjuration spell that forces a creature to return to its native plane.

Effect
This spell forces an extraplanar creature back to its proper plane. Add the creature's HD to its saving throw and subtract your level as well. If the spell is successful, the creature is instantly whisked away, but there is a 20% chance of actually sending the subject to a plane other than its own.

Arcane Focus
Any item that is distasteful to the subject. (For example, to dismiss a fire elemental, one might use a flask of water.)