Intelegent casting rings are kind of rough, but they have a limit to how often they can cast the spell.
The sanctuary has to drop if the player attacks that round (untill their next non-offensive round), even if they don't have to activate it.
In one campaign, the GM gave me an intellegent bow that could cure serious 3 times a day. I think that was more a way to keep my low HP wizard from dying, as well as a balance to a lack of a true pure cleric in a 4 player campaign. I've only used it in a BBEG combat and hense, was one of the only 4 out of 8 players and NPCs to survive (We waterwalked to try to gain supprise, and the octopuss one of the head BBEGs had controlled was supprisingly much more effective than the GM had planned it to be).