currently to mitigate physical damage there is multiple skills for example:

protect (weakest of them all)
stoneskin (100% mitigation with max absorb limit)
defender (must have for tanking / off tanking)
rampart (IMO this is an emergency skill)

while protect is basic mitigation spell it really does minimal reduction but it does last longer then stoneskin & rampart. even though defender does increase defense it also deceases offense but it does the job that it is suppose to do and really help out on the physical mitigation. defender should be one of the must have for tanking or off tanking, the only draw back is that it is a self cast only and your tank / off tank should be using this but that isnt always the case.

but for magic attacks there is only currently only shell which doesnt do enough mitigation on magic damage. but i would love to see elemental bar spells like:

bar-water
bar-fire
bar-stone
bar-wind
bar-ice
bar-lightening

even though the increase was very minimal but i like to also see bar-sleep, bar-slow, etc... but the value of Bar spells need to be increased in compare to its counter parts in FF 11.