In the previous Mechanics post, I explained how to hold threat for beginning DK tanks. In this post I will explain how to stay alive through the tight spots you will undoubtedly get yourself into.
The basic and most important cooldown that DKs get is this blog's namesake, Icebound Fortitude. This spell is available at a trainer at level 62 and is the one-spell-fits-all answer to bad things happening. Unimproved, it reduces all damage you take by 20% for 15 seconds and is on a 1 minute cooldown (soon to be 2 minutes in 3.2). Deep frost DKs can improve it by up to 6 seconds of duration with the Guile of the Gorefiend talent, and for the rest of us, the Tank-T7 four piece bonus increses its duration by 3 seconds. Additionally, it scales to your Defense skill, gaining about 0.107% damage reduction per defense skill beyond 400, making it 34.98% if you are defense capped at 540 defense.
Using icebound fortitude couldn't be simpler, it is an instant cast, and requires no runes, only runic power. As long as you haven't been spamming Death Coil or similar, you should almost always have the resources to cast it whenever you need. Since the cooldown is so short, usually you do not need to worry about saving it for the perfect time to cast, since it will probably be back up by the time you need it again. It is best used to give your healers a few moments to react to big shifts in your incoming damage, and many appreciate you announcing about 5 seconds before your Icebound will end, so they can be ready for the damage to spike to where it would have otherwise been.
The other cooldowns that will be important to you will depend on your build. Frost DKs have the excellent Unbreakable Armor which, unlike Icebound, reduces damage taken by a fixed amount, making it incredible for tanking large crowds of adds, or enemies that hit very quickly for small amounts of damage per hit. Additionally, Unbreak increases Strength by 25%, increasing your threat output and your parry rating.
Lichborne, also in frost, is rather useless. It has recently been nerfed to no longer add a miss chance to incoming attacks, and only makes you immune to Sleep, Fear and Charm, none of which are common in current raids.
Hungering Cold can also be considered a defensive cooldown, but is typically only useful for dealing with trash or a boss's adds. It freezes all targets within 10 yards, preventing them from killing you or your raid members for that long.
In blood, Rune Tap is often overlooked, but can be very useful when fully talented and glyphed. Unimproved, it is a 1 minute cooldown that heals 10% of your Heath for 1 blood rune. It is an instant cast, and is not on the global cooldown. But, with Improved Rune Tap, this becomes 20% of your health on a 30 second cooldown, and when glyphed it heals 22% of your health, and heals everyone in your group for 10% of their health. When used properly, it can save you long enough for a heal to get off, or save your party so you don't end up trying to solo.
Mark of Blood is pretty meh, but well worth the one talent point. When cast on an enemy, the next 20 times it deals damage, it will also heal its target for 4% of their maximum health. In a 5man, this can be a lifesaver if cast right before the boss does an AoE or a DoT. In raids, it is usually not quite as useful.
Vampiric Blood in deep blood is a powerful cooldown, which increases your max health by 15% and increases your healing recieved by 35% for 20 seconds. Unlike Icebound, it doesn't allow your healers much longer to react, but can be great to chain off the end of another cooldown, allowing your healers to heal through damage much more effectively.
Anti-Magic Shell is pretty meh even when talented in deep unholy. Normally it reduces incoming magic damage by 75%, protecting a maximum of 50% of your max HP. When talented with Magic Suppression, it is still capped at 50% of your health, but does block all incoming magic damage. The other half of Magic Suppression reduces all incoming magic damage by 6%, all the time. For tanking fights with a lot of magic damage, the talent is worthwhile, but the cooldown doesn't have nearly the impact of the others you have available. What it is good for is not mitigating damage, but protecting you from debuffs. The other half of the spell makes you immune to harmful magic debuffs while the spell holds. This can be great for causing a stacking debuff to fall of of you, or prevent a particularly annoying debuff from applying in the first place.
If you do go deep enough in unholy to talent AMS, you can gain access to Anti-Magic zone, basically giving you a second AMS. It too absorbs 75% of magic damage, and is capped at about the same amount of health (but it scales to attack power, not HP). The other benefit of the zone is that it can be used to shield raid memebers from AoE.
Also in unholy, Bone Shield reduces all damage taken by 20% for the next 4 hits. With the glyph, this becomes 6 hits. Bone shield is also pretty meh, as it tends to end very quickly, but can be great in conjunction with parry or dodge boosting cooldowns, as they extend its duration. The other nice thing about bone shield, is that it lasts for up to 5 minutes, but the cooldown is only 2 minutes, allowing you to enter battle with it already active, and also ready to cast.
And finally, Army of the Dead, which is possibly the most powerful defensive cooldown you posess after Icebound. For the 6 seconds while you channel it, it will reduce all damage you take by an amount equal to your parry plus your dodge chance. For me, this is around 55%, which is greatly more powerful than Icebound Fortitude. Additionally, the ghouls you raise can taunt and tank any trash in the area, preventing it from killing you or your raid until the ghouls die. This spell can even be used to build threat, if you taunt a mob that the ghouls have been taunting back and forth, it will skyrocket your threat to several hundred thousand above anyone else. The trick is that it requires one of each rune, and is on a 20 minute (10 when talented) cooldown, and can definitely only be used once per fight. Use it wisely, and be sure you have your runes ready for when you plan to cast it.