Not entirely sure if this is working as intended and i did search around for this "Spell Reflect" and "Anub'arak".
Lately i have been trying to get my trinket off the 2nd boss for my tanking set (So far 6 days in a row its the stupid mail pants, and yesterday it bugged. It died to the mobs and de-spawned the corpse. Anyways...
On the last boss of the Azjol Nerub dungeon there is a boss that casts "Locust Swarm" which is auctually Reflectable. As a warrior, everytime his cast time for "Locust Swarm" is at 0.5 sec left, i hit Spell Reflect, and for the entire 5 seconds, locust swarm is reflected. It ticks for about 700 damage a second i belive on heroic, so it helps a lot for trying to get that achievement. I have not tested this with "Improved Spell Reflect" though. If it works, everyone in the group will be reflecting his locust swarm (Because when this spell is reflected, it doesnt consume spell reflect in the process) so u can get him down much faster. 700 DPS x 5 reflects = 3500 DPS for 5 seconds! Thats 17500 in 5 seconds on him.
(Sorry if this becomes a wall of text)