I did If the spell target is an item or PC they light up for the duration. If it is the ground, then it reveals any creatures in stealth in the area of effect and gives them a hide penalty for a few rounds.  I'd have to look, but I think the area of effect, penalty and duration grow with casting levels.
Sound really cool.
In this way even a cleric that does not have many point in spot / listening,has any chance of countering cser.
I do not know if I am able to accomplish something like that ...in the past i tried to change the spell "color spray" in a way that if the creature in stealth mode was hit by the beam, the stealth mode will disable.
But I got poor results.
I made many changes in my module in order to make useful all spells and all feat for the pvp, but some changes are beyond my abilities.