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It's parried - Hammer is technically a ranged attack which is why it can sometimes lag up if your just out of range or the mobs move on you as your pressing it. US players probably wouldn't notice it but when you have a 200-600ms ping you see it now and then. :)
You need 24 expertise to not get parried by bosses. You need 60 to not get dodged or something like that. This is not feasible and there is no point trying to achieve that.
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There is a nice staff in pit of saron named something like Gargoyles broken femur.
I got this on my warlock and it has over 100 hit rating on it (may even be as high as 124).
If you are willing to give up your shields on the shaman then this should go a long way towards
hit cap for raid bosses.
Edit: Item is Engraved Gargoyle Femur.
110 stam, 121 int, hit rating 113, haste 86 and spell power 550.