My oldest son was considering how clerics Turn or Rebuke Undead recently. We discussed the possibility of 'Turn Wars' where good and evil clerics use Turn Undead (or Rebuke Undead for the evil cleric) in a sort of proxy war with zombies shuffling back and forth as the good cleric Turns them and then the evil cleric cancels the Turning by Rebuking them over and over until one or the other misses his die roll.
Then he mentioned,
"Clerics should be able to rebuke paladins."
That certainly makes sense - evil clerics can, after all, Turn paladins. Heck, I would argue evil clerics can Turn things like coatl, lammasu, and other Good beings with ties to either the Positive Material or Upper Outer Planes. So if an evil cleric Turns a paladin it makes sense that a good cleric could then cancel that by Rebuking the paladin.
He went on,
"So why couldn't a good cleric Rebuke a paladin to prevent him from committing an evil act? Or a Lawful Good cleric do the same to prevent him from performing a chaotic act?"
Hmmmm. Sure, why not?After all, the chaotic or evil act must come from some wavering of faith or, worse (and more likely) a Charm of some sort.
So after a bit of discussion we worked it out this way.
1) The paladin must be on 'good standing', i.e., not have lost his paladin status
2) The cleric must be Good to Rebuke a paladin from committing an evil act or to negate the Turn of an evil cleric. If the cleric isn't Lawful Good this is at -1.
3) The cleric must be Lawful Good to Rebuke a paladin from committing a chaotic act.
4) If the paladin is acting chaotically or evil because of a Charm or similar magic a successful Rebuke gives the paladin an immediate save with a bonus equivalent to the difference between the number needed to turn and the number rolled.
Example #1: Sir Roland (a 5th level paladin) and Brother Eirik (a 7th level cleric, LG) are part of an adventuring party clearing out a defiled catacomb. Suddenly an evil cult leader (7th level cleric, CE) appears on a ledge and Turns Sir Roland, rolling a 17 - Sir Roland is compelled to turn and flee.
Brother Eirik, however, calls upon God and Rebukes Sir Roland, rolling a 19 - the Paladin turn back to face the cultist filled with holy resolve. The cultist tries again but rolls a 3 and failes. Sir Roland moves to kill the miscreant.
Example #2: Sir Roland and Brother Eirik are returning to their home abbey from the catacombs when a lovely dryad approaches. He mystic powers envelope Sir Roland (who rolls a 3 on his saving throw) - his sword drops from numbed fingers as he prepares to abandon his services, forget his oaths, and leave with the tree spirit. Brother Eirik clutches his crucifix and calls out to Sir Roland, Rebuking him. Brother Eirik rolls a 19, 3 above the required 16. Sir Roland rolls again, adding +3 because of the successful Rebuke, and gets a total of 22. No longer Charmed he retrieves his sword and continues to the abbey.
Example #3: Telemar the Paladin (2nd level) is serving as a guard at the Cathedral when the powerful evil mage Alyndera attempts to steal the evil Staff of Black Magic from its vaults. Alyndera casts Charm Person on Telemar, who rolls a 9. Using a Forget spell and her high Charisma Alyndera convinces Telemar to open the vault for her. As Alyndera prepares to remove the wards protecting the staff Archbishop Gregory (16th level cleric enters the vaults, alerted by a Glyph.
"Telemar, that is the demon disguised as the archbishop I told you about! You have but a moment before he kills us all!"
Telemar draws his sword and strides toward the Archbishop. Gregory, knowing time is of the essence, utters a prayer and Rebukes Telemar, rolling a 12; since Gregory has a T result to Rebuke Telemar the young paladin gets a new save at +12.
Telemar faces Alyndera with a stern look as the Archbishop joins him.
Will this come up often? No, but it is an interesting element to add depth to your campaign.