In my current setting, the local temple has a permanent [Zone of Truth](http://www.d20srd.org/srd/spells/zoneOfTruth.htm) effect in the main hall. While I intended the effect to be an innate quality of the stone used to build the temple, there is no permanency option noted on the SRD.

In reference to will saves against the emanation, it simply states that 

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> Each potentially affected creature is allowed a save to avoid the effects when the spell is cast or when the creature first enters the emanation area.
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This would make sense in regards to a non-permanent spell.

However, if this effect exists essentially forever, *does any one creature only ever get a single save against this particular zone of truth, or do they get a save for every exposure to it?*