Accuracy isn't going to help you very much with your DPS as a tank. It's a multiplicative stat, and since tank DPS is already quite low, the occasional miss doesn't actually have a very significant effect over time.
Your best bet is to push your damage dealers a bit more. My advice in no particular order:
- Practice getting back from the Sandstorm as quickly as possible. There is no position which requires more than 40 seconds to return, and most require 30 seconds or less. All classes and specs are capable of this.
- If you're using Snipers, make sure they're using Entrench during the channeled moments of their rotation whenever it's up.
- Move quickly between shield points. Keep damage up as much as you can, but the priority is speed.
- Only put a single DPS on Xuvva duty, and then only part-time. Especially if you have Flyby available to you, half of a DPS should be more than sufficient. Experiment with giving the Xuvvas less and less attention until they eat the shield. Spend as little time on them as possible. Ignore them for most of the 4th shield.
- Have your healers DPS a little. Thanks to the SA double-proc bug, it will actually help their healing to DoT the boss periodically (unless they're a merc). A single shield is trivial to solo-heal. Have one of your healers DPS full-time in the fourth shield. I've actually healed this fight successfully with a sage who spent nearly *all* of her time DPSing. It's not that terrible if you have decent tanks, good positioning and proper Womp Rat management.
If all else fails, the solo tanking suggestion is a pretty good one.
The DPS check on this fight *is* fairly hard. My guild has some very high parsers in our DPS group (all except our Focus Sentinel are over 3k, and one is at 3.2k), and we still consistently come right down to the wire. We can kill him before the shield falls in the fourth position, but it's close. Our first few kills happened well after the shield fell, relying on unused personal shield orbs and gunslinger raid shields.
If you're consistently getting him to 5%, then you've seriously got the fight. Just sharpen up on a few things (especially the Sandstorm return and a bit of healer DPS) and you'll down him.