Hold Portal

This spell magically bars a door, gate, or valve of wood, metal, or stone. The magical closure holds the portal fast, just as if it were securely closed and locked. Any extraplanar creature (djinn, elemental, etc.) with 4 or more Hit Dice can shatter the spell and burst open the portal. A wizard of 4 or more experience levels higher than the spellcaster can open the held portal at will. A knock spell or a successful dispel magic spell can negate the hold portal. Held portals can be broken or physically battered down.