Seal Portal

(Manual of the Planes, DnD 3.0)

Abjuration

Level: ; Sorcerer/Wizard 6
Components: V, S, M
Casting Time: 1 action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One interplanar gate or portal
Duration: Permanent (D)
Saving Throw: None
Spell Resistance: No

You may permanently seal an interplanar portal or gate.
If cast on a portal, the spell prevents any activation of it, although seal portal may be dispelled by a dispel magic spell.
A knock spell does not function on the sealed portal, but a chime of opening dispels seal portal if seal portal was cast by a spellcaster of lower than 15th level.
In addition, the ability of the gatecrasher prestige class to open portals may be able to break through a sealed portal, but if the first attempt fails, the gatecrasher can't try again.
Once the portal is opened, seal portal does not return and must be cast again.
Material Component: A silver bar worth 50 gp.