Surelock

Surelock was specifically designed to protect against unwanted plane-spanning portals. As long as it's in effect, the spell seals all gates and portals that reach into other planes. The spell does not affect movement abilities within a single plane, so a teleport spell is unaffected by it (since it can't take a body to other planes). However, permanent, temporary, and shifting portals cannot open within the area affected by the spell. Likewise, plane shift and astral spell don't function within the area of effect. A gate spell cannot pull a creature into or out of the affected area. Any attempt to use any of these powers results in automatic failure — a spell to that effect would be wasted and a charge from a magical item would be lost.

When cast, surelock spreads out in a radius from the caster to the full extent of its area of effect. It is not possible to exclude portals within this area; everything is affected equally. Nor can the effect be lowered, even by the caster, without the use of dispel magic. Once cast, the area does not move — although originally centered on the priest, it does not follow him around thereafter.

Despite the various gate ward and gate seal spells used by wizards, this is still — by far — the most potent ward against interplanar travel. Its radius of effect, duration, and ability to block spells as well as actual gates and portals makes it clearly superior. Despite this, note that in Sigil, the Lady of Pain has absolute control over the city's portals and may choose to overturn the spell's effects at her whim.

The material component for this spell is a crystal key that must be shattered when the spell is cast.