Go Long

This should be removed from Glory of the Orgrimmar Raider - seriously.

When [npc=71479] enters his Desperate Measures phase (66% and 33% health), he'll place [spell=144365] on a random raid member, rooting them in place and summoning [npc=71478] which will focus on them.

[spell=144365] can be given to other players via a special action button, so this can be done by having five or more raid members stack in a square/pentagonal/hexagonal shape and gradually move the debuff around the room while the rest stay in the middle.
The range limit for transferring [spell=144365] is 40 yards, so plan accordingly.

Do keep in mind moving the debuff will apply a stack of [spell=144176] on your entire raid, so the damage will gradually ramp up.

Currently, if you are dead when the bosses die, you do not earn the achievement. Very annoying.

Edit: A GM did provide me with the achievement upon ticketing it, as I was able to give them the name and server of one of the characters that were still alive (and received the achievement) and the GM was able to verify that I had tagged all three bosses.

Edit 2:
5.4 Hotfixes: October 29

The Fallen Protectors
Resolved an issue that prevented players that have died during the encounter from receiving credit for the Go Long achievement.

Supposedly the achievement has been fixed, so I'm marking this out of date.