Efficacious Monster Ward

This spell prevents monsters of 2 or fewer Hit Dice from entering the area of effect. Such creatures are allowed a saving throw; success indicates that they avoid the spell's effects and are able to enter the area of effect.
The spell affects a cubic area whose sides equal the caster's level times 10 feet (for example, a 9th-level caster could affect an area equal to a 90' x 90' x 90' cube).
Monsters within the area of effect when the spell is cast are not affected; however, when they leave the area of effect, they cannot return. Monsters outside the area of effect can hurl rocks, spears, and other missile weapons at targets inside and can also cast spells into the warded area.

[Tome of Magic]

Sphere: Wards
(Abjuration)
Level: 3

Range: 30 yards
Components: V, S, M
Duration: 1 round/level
Casting Time: 3
Area of Effect: 10-foot cube/level
Saving Throw: Negates

Material Components:
the priest's holy symbol and a pinch of salt