Okay I have thought about clemency "not stepping on healer's toes" that would go well with defensive tank.

One second cast time. Paladin and the target share 50% of healing for 10 seconds. It could also provide a small shield.

Now if you would see somebody dying you would pop it up and any heal that would heal you would also heal the target for 50% and any heal that would heal the target would heal also you for 50%. Basically the healer wouldn't risk to wipe the tank while saving somebody else.