Or make it channeled!
Discipline Priests OHSHI- Button
I'll suggest:
Power Word: Barrier Rank 1
31% of base mana 40 yd range
Channeled 1,5 min cooldown
Draws on the souls of all party or raid members to shield the 5 lowest health friendly party or raid targets which will absorb up to 2230 damage. Each additional 1,0 second channeled will shield 1 additional party or raid members with the lowest amount of health, and reinforce the shields of those already shielded by an additional 10%. The Priest must channel to maintain the re-casting of new shields. The shield will not be reinforced more then 50% of it's original effect. Up to a maximum of 15 targets may be shielded at any time. Channeling lasts a maximum of 10 seconds. Shields lasts 15 seconds before automatically breaking. May only be cast when in combat. Causes the
http://www.wowhead.com/?spell=6788.
To break it down to you:
-Instantly shield 5 low-hp members.
-Every second an additional shield to ANOTHER low-hp member
-Every second shields which still last get stronger by 10%
-Shield's power increased is a maximum of +50%
-Shields last 15 seconds each (but get refreshed whenever you maintain the spell, and reinforce the current shield)
-Max 15 targets
-May only be cast IN combat
-Causes
http://www.wowhead.com/?spell=6788 to prevent stacking of the buff.
Priest also get's to chose to just instantly shield 5 targets, abort the spell and simply resume normal healing.
OR
Maintain the spell, and instantly shield 5 + 1 target every second for a total of 15 targets