[jere]

Source: Trysha Concencrate, exorcism, and Holy sheild are the only things pertaining to magic with a prot paladin. Seals, Judgements, etc. are under expertise

Just wanted to clarify this as incorrect.

While Consecration, exorcism, and Holy shield are all 'spells", judgements are not under expertise (as stated above). Tanking seals are affected, but only in the sense that the melee swing has to land to do what the seal does (though that is pretty moot for SoV as it has to land sometime outside a 15s widow to fall off).

Basically:

Expertise
HotR (Deflect is reduced by expertise and is the replacement for parry)
Melee
Seal Application Attempts (melee strike has to land afterall)

Melee Hit -- 8% cap
Melee
Shield of Righteousness
HotR
Hammer of Wrath
Taunt (17% cap though)
Judgement

Spell Hit -- 17% cap
Holy Shield
Consecration (yes it is now affected by hit -- not so much in BC days)
Exorcism
SoV stack application (assuming the melee hit lands)
SoV 5-stack damage

That's not an exhaustive list

As for is it worth it to stack Expertise to a certain cap, well that is up to the person honestly. I try to hit the dodge cap, but that isn't hard (as expressed above). For threat reasons, there are much better stats to stack. Check this thread out for more details:
Maintankadin • View topic - Theck's MATLAB TPS analysis (A Jonesy derivative work)

[Martie]

Source: neomasterc Im currently a DK tank with 31.5k hp unbuffed, bout 28% dodge, and 20% parry. with raid buffs+flask i have bout 40k hp. should i continue to gem for stam?

Yes you should.

[Undeathguy]

Isnt it better to gem avoidances, as its better to not take the hit than to take the hit, even if you have a little more health.

[Warlikes]

Sure its better not to take the hit. But the problem is you cant control when you take a hit. Avoidance is not something that is going to be there every hit. The only thing you can depend on to be there every time you take damage is health and if you have more health left after the hit then you need less healing to take the next one. But avoidance verse stam has been argued into the ground in other threads already.

[Tharr]

I think it's better to stack health so you comfortably survive then go for avoidance or threat. How much health that is I leave up to each and everyone to figure out themselves since I can't say what you fight or how your raid looks or how good your healers are and whatnot.

Generally though, healthstacking works. Avoidance does to, as long as you don't neglect your health. And as always, different fights require different gear.

[Martie]

Source: Undeathguy Isnt it better to gem avoidances, as its better to not take the hit than to take the hit, even if you have a little more health.

At 50% avoidance, there is a 25% chance a boss will hit you twice in a row.
At 60% avoidance, there is a 16% chance a boss will hit you twice in a row.

Nothing you can do will make it unlikely that the moss hits you twice in a row. Stamina stacking increases your chances of surviving those two with minimal healing. (For a DK even without healing in many cases.)