This past couple of weeks, I've been experimenting with tanking in my standard fury spec. One of the effects of patch 3.1 and dual specs that I hadn't considered until then was that I would most likely have a DPS spec and a tanking spec, both optimized, and therefore I'd probably never try to tank in an offspec again. When asked to offtank in a raid or even to MT for one reason or another, I wouldn't try and do it in fury or arms, I'd use my dual spec and swap over to prot, with prot glyphs ready to go. And while this is on the whole a good and positive change, I'm stubborn and crazy enough to look back on my long and storied (well, long anyway) career and all the times I've tanked in an arms or fury spec, something I will probably never do again come 3.1.
Up until BC launched, in fact, I often tanked as arms or fury. My standard raiding spec back before BC was either 31/5/15 or a deep fury DW build that didn't even go the 15 in prot for Defiance. Back then, the extra threat from Defiance wasn't even strictly seen as necessary. Sure, if you were going to go deep prot to MT for a guild you'd pick it up, but a lot of warriors didn't even bother. I realize now that saying "I main tanked up to C'thun as 31/5/15" is the old warrior's version of saying "We walked uphill both ways in the snow" nowadays, but it's still accurate. I didn't go prot until we were working on Naxxramas 40. Back when I was seriously considering swapping my human for an NE warrior on a different server, I ran a lot of instances as pure fury as a tank, working the rotations as best I could figure out for holding threat.
So for the past few weeks, as we've moved from farming to complete and total annihilation of the current raiding content, I've been playing with tanking as fury again. It's fair to say that a fury DPS spec isn't really anywhere as good as a tanking spec as a dedicated prot spec, and I wouldn't recommend that your average TG warrior just slap on a shield and wear his DPS blues into the heroics (much less 10 or 25 man raids) but in general I've been successful, tanking up to Kel'Thuzad with a fury spec. This is the spec I've been using alliance side, while on my tauren I've played with this spec as well as this arms spec. (The Arms spec I'm using is not my main Arms DPS spec.) I use Mace Spec because I have the Split Greathammer as my tanking weapon.
So far I'm finding both the fury and arms specs have their ups and downs. Bladestorm is actually a lot of fun to use as an AoE tanking tool, and when I'm fury tanking I enjoy using a 2h weapon (usually The Jawbone) and a shield. I find tactical mastery makes fury tanking easier (you can switch stances for a Retaliation in multi-mob pulls more easily as well as get more threat out of those high-rage Bloodthirsts) and that I'm weaving Shield Slam, Revenge and instant-cast Slams into my tanking rotation. To be fair, it helps immensely if you can get a hunter to misdirect whenever its up or a rogue to cast Tricks of the Trade on you (we have a rogue who has me as her focus when I'm tanking so she can more easily ToT me - I always try and time a thunder clap and shield slam or Bloodsurge Slam for when I see the jacknife over my head) and it generally is the case that DPS has to take it easier on me when I'm not specced prot, but with Challenging Shout I can usually grab peels pretty easily and everything's dead by the time it wears off.
With the basic threat baked into Defensive Stance, the real liability of a non-standard tanking spec is all the tricks that you lose from protection. No Vigilance, no Shockwave, no Devastate, no charging in combat (you can stance switch for an Intercept and Intervene is still available, of course), none of the added magic reduction of Improved Defensive, the excellent multi-mob utility of Damage Shield, your base block value is lower due to your loss of Shield Mastery and you can only Shield Block once a minute instead of once every 40 seconds. It's fair to ask why anyone would want to tank without the plethora of goodness that protection provides a tank.
For myself, it's been partially nostalgia, partially the awesome factor of getting to tank with a 2h and a shield and play with new spec ideas that I may never use (this one is getting a test run today in Naxx - 10) and partially pure stubbornness. I would never recommend that anyone sign up to tank for a raid in a spec like this, especially if your guild doesn't know you're doing it and doesn't ridiculously outgear the run. I've had the benefit of tolerant guildmates who've been willing to do heroics and raids with me while I've played with these specs, I wouldn't foist off my bizarre fury tanking ideas as we head into Ulduar. And with dual specs, frankly, I don't imagine I'll ever be asked to switch to tank gear for a couple of bosses ever again without switching to a prot spec with the proper glyphs all set and ready to go. For one thing, with the Titan's Grip changes, why would I tank with a 2h weapon and a shield and reduce the damage of my Thunder Clap, Shield Slam, and Revenge by 10%? (I'm pretty sure that's got nothing at all to do with that change, just saying.)
But to a degree that's another reason why I'm so interested in playing with this now. First off, I may never have such a perfect storm of bored guildmates who've gotten all of the gear and achievements they want willing to just try out weird things like this. Secondly, one of my big concerns with 3.1 and the rise of dual specs (and the rumors of triple specs in the future) is that we're going to lose a little bit of that spirit of "Heck, let's just try it" that has led to me finding myself in tanking gear on Malygos because our MT disconnected and couldn't get back on and no one wanted to wait for me to hearth and respec and come back.
With the advent of patch 3.1, this is probably your last chance to really mess around until Ulduar is on farm. Why not take advantage of it? In a couple of months you'll be dual specced anyway, this is the last real chance you have to take yourself out and see just how hard you can fold, spindle or mutilate that DPS spec. For that matter, slap on some DPS gear and see how high you can get your Shield Slam crits: there's no reason tanks can't play around as DPS, too. Properly geared, you may never match a dedicated DPS warrior, but you can still have some fun. And with us all waiting for new content, you have to have fun where and when you can.