Destruction Staff is extremely important on a Tank and it’s actually more useful than a One Hand and Shield if you look at the number of useful skills and passives.
The main reason this is used is because of the Elemental Blockade ability and the weapon glyphs. When you use a Staff, the weapon glyphs you use have double the value that they do on a 1 Handed weapon.
You should almost ALWAYS use an Infused Staff with Crusher Enchant since it provides a large enemy debuff extremely easily.
When you place your Blockade it will activate the Crusher debuff on the target that is closest to you. The enchant will stay on the enemy for 4 seconds and because the duration of Blockade is 15 seconds, even when you are on your front bar Blockade will automatically continue to proc the Crusher Enchant multiple times over the duration of its ability and you need to try and recast Blockade on cooldown to keep the Crusher enchant automatically reactivating itself on the target.
There are other abilities that you will need from the Destruction Staff skill line for various content such a Crushing Shock for Ranged Interrupting, Elemental Drain for debuffing and helping your Magicka DDs sustain via the Minor Magickasteal.
You should use a Frost Staff as they are the most useful.
Frost Staves: These are the most useful weapon to use as they offer you actual defence as a Tank and there is very little difference to using a Frost Staff compared to a One Hand and Shield. You get increased block mitigation, reduced block cost when using a Frost Staff for starters, and you have a unique debuff provided by a Frost Staff called Minor Brittle which increases the enemy critical damage received by 10% which is a big DPS boost for your group.
Frost Clench and Frost Pulsar are incredibly useful skills for a Tank. Clench offers a Taunt, Major Maim, Minor Maim and Minor Brittle as a single target and is great for boss fights. Frost Pulsar causes AoE chilled, AoE Minor Maim, AoE Minor Mangle, AoE Minor Brittle and AoE Minor Protection. When you also combine Frost Pulsar and Frost Blockade you gain AoE Minor Breach.
Some builds like to use the Tri-Focus passive but generally it’s advised not to use it until you are experienced with Tanking to utilise it properly. When using a double frost staff setup you might use it.
