1. BoP on Overaggro
This macro is divided into 2 different macros, one is "Foucs target" and one is the "BoP cast" macro.
The "Focus macro" will, guess what.. set focus on a target. So, before each boss fight you should target the boss and then click this macro (OBS! this macro saves the name of the target so if there are more than one target with the same name, for example on Skeram and his clones, this wont work 100%)

/script t=Tg1 or""c=IsShiftKeyDown()if(c)then TargetByName(t) else t=UnitName("target")or"" end ChatFrame1:AddMessage(" "..(c and("Targeting: "..t)or("---Focus set to: "..t)))Tg1=t

Once you set the focus on the boss you are now able to use the other macro, the "BoP cast" macro.
This macro will, when its pressed, target your focus target, check if he/she is targeting a warlock or a mage (feel free to add more classes here, but imo you should only keep this for Warlocks and Mages). If he/she does target a Warlock or a Mage you will target that target, cast a BoP and whisper the target "OVERAGGRO - BoP casted!" and then re-target the boss.
/script TargetByName(t)
/script class=UnitClass("targettarget"); if (class=="Mage") or (class=="Warlock")then TargetUnit("targettarget"); CastSpellByName ("Blessing of Protection");SendChatMessage("OVERAGGRO - BoP casted!","WHISPER",nil,UnitName"target")end
/script TargetLastTarget()

So basically before each boss encounter you think this is worth having(broodlord for example :P ), you target the boss, click the Focus macro and later when/if someone overaggros the boss u simply click the BoP casting macro and the boss will return to the tank.
You can ofc include this macro to your casts so that you always checks for an overaggro before casting a heal.

2. BoP with a safety check
This macro will check what class you are BoPing. Its always good to be sure you don't miss click and BoPs a tank/warrior that's supposed to have aggro.
/script class=UnitClass("target"); if (class~="Warrior") then SpellStopCasting(); CastSpellByName ("Blessing of Protection"); end


For suppression room or other places where you got assigned BoP targets I would recommend you all to add /target "name" and after that a /script TargetLastTarget(), making you able to just press one button as soon as you see your assigned target getting low, or when we got huge whelps pulls:
/target "name"
/script class=UnitClass("target"); if (class~="Warrior") then SpellStopCasting(); CastSpellByName ("Blessing of Protection"); end
/script TargetLastTarget()

(feel free to remove the TargetLastTarget macro if you want, but I like to go back to my last target since I'm always targeting the Mobs and healing with grid :D)
/cheers