OK let me clarify what you're looking for so that others who read this thread can really understand. You're looking to find out which points in protection help PvP survivability as a holy paladin. Easy enough once you clarified yourself.
Guardian's Favor - Reduces the cooldown of your BoP. Chances are you won't use it more than once in arena, but you might and this will help at least give you a chance to use it twice.
Improved RF - This reduces all the damage you take by 6%. It may not save your life, but any straight up damage mitigation in PvP is a good thing.
Improved Concentration Aura - The actual increasing of the damage interrupt won't affect you as much since you'll have 100% from combination of the base aura and holy talents, but the nice part about this (when considering only yourself) is the fact that it reduces the time you are silenced and interrupted, which greatly extends your survivability
Stoicism - Not really my cup of tea, but this could help your survivability in that it makes it harder for people to stun you while casting a heal spell.