Ok here's my one. It's very similar to a couple mentioned before but has a slight twist.
Item: Leftovers / Shell Bell
EVs: 252 SDef / 252 HP / 4 Atk
-Fire Punch / Brick Break / Earthquake / Aerial Ace (whatever coverage you want)
-Stone Edge / Rock Slide (STAB - [power or accuracy])
Shell bell is more for if you want to use your leftovers on one of your other Pokemon. Since this Ttar is going to be dishing out a lot of damage shell bell will provide a good amount of healing anyway.
There may be a better item to use than these, but since Choice items aren't good with dragon dance and focus sashes aren't needed (explained below) I havn't come up with anything better yet.
Perhaps an expert belt if you don't have anything better to use it on.
So the thinking behind this is that with all those SDef EVs + careful nature + the SDef boost from sandstorm it should easily be able to take multiple hits from special attacks so send it out against a special attacker (preferably without focus blast). They hit it, it shrugs it off and dances. The opponent has a choice then of either hitting it again (not usually a great plan) or switching to something with a bit more phys (should have done that last turn). Either way Ttar now has 2 dances up and at this point there's not much that can stand up to it.
Using this set up I've managed to survive Focus Blasts from Alakazam with over 1/4 of my HP remaining so there's not really any special attackers out there that can threaten it enough to need a focus sash.
Its main weakness is if someone switches straight out to a physical attacker with a fighting move and enough speed to beat it while dragon danced, but most people will try hitting it with at least one special attack before realising how useless that is.
Hope you like it, and if you think of a better item for it or any major flaws I'd love to hear it.