I always used to tank Unhoy as well. Bone shield was difficult to pass up along with all that AoE threat for heroics. Since the changes in 3.1 though, Bone Shield doesn't hold quite the allure that it once did, simply because of the 2 minute cooldown on it.
For me, a change was necessary since I didn't feel like I had enough avoidance (parry and dodge for those not familiar with DK avoidance) to be able to keep Bone Shield on long enough. Once I get some more avoidance gear in Ulduar, I may switch, although I've heard some things about Unholy single target threat that gives me pause.
For now, I'm using 12/52/7 which seems to be working okay. I have like 28% dodge and 22% parry with buffs, so it's not bad. I just like the extra mitigation so the damage is a bit more consistent and not as spiky when my cool downs aren't up. My gear is all hand me downs from the tanks that already had stuff, so it all needs some improvement, but /meh... it'll come around.
Here's to hoping Worldcarver drops off of Ignis when we finally get him down. Would be a nice step up from Death's Bite
Dunno if this helps, but I'll keep looking for some unholy specs for you. Tankspot.com is a good place to start.