Getting Ahoo'ru is all about A) having most or all the raid buffs and decent enough gear (anything 520+ with a 530 (upgraded) weapon should be fine, below will be rough), and B) handling the first phase properly. Try to get all 3 adds active as quickly as possible and don't overDPS one if it's going to charge soon. It's helpful to let sting/black arrow/pet damage trigger the charge while you attack the next one as long as you're in a position to not be killed by the charge.
In phase 2 deterrence will completely negate the divine orbs; just pop it, run through, cancelaura. Save readiness until after the first set of orbs and you can deterrence the second set too. Don't forget that he casts the aptly named Complete Heal as well, make sure you interrupt it. I didn't even bother trying to get threat on my pet and just face tanked it; spirit bond and a healthstone was more than sufficient. Glyph of liberation can help too if you need it.
Oh also, don't attack him when he spawns at the very start. He automatically heals to full while in his shield so attacking him, even if you aren't using any focus, will just waste your trinket and set bonus procs.