Hallow

If you’re of a religious bent, this is a perfect spell to help protect your stronghold. When cast by a 9th-level caster, the spell can cover a 90-foot-radius circle (which would completely cover a relatively compact stronghold of about sixteen spaces, or more if you build in three dimensions).

Not only does hallow provide a permanent magic circle against evil throughout the affected area, but any body buried there cannot become undead. If a cleric casts the spell, it also provides a +4 sacred bonus on turning undead and a –4 sacred penalty on commanding them.

Best of all, you can fix a programmable spell to the site with a duration of one year. If you do this, you must pay the cost to have the extra spell cast, plus another 1,000 gp per level of the spell. You can designate whether the spell affects everyone, only creatures that share your faith or alignment, or just creatures that have a different faith or alignment.

Some common choices (and the cost for an NPC spellcaster to provide them) are listed below.

Spell	Additional cost (not including hallow)
Bane (on enemies)	1,010 gp
Bless (on allies)	1,010 gp
Daylight (cleric version)	3,150 gp
Detect evil	1,010 gp
Discern lies	4,280 gp
Dispel magic (on enemies)	3,150 gp
Invisibility purge	3,150 gp
Negative energy protection	3,150 gp
Remove fear (on allies)	1,010 gp
Silence (on enemies)	2,060 gp
Tongues (cleric version)	4,280 gp
Zone of truth	2,060 gp

Casting: 1,450 gp (Clr9 or Drd9) plus additional cost for extra spell (see above)