For tanking on a warden, you shouldn't need the attack duration runes to hold aggro, if you think you might, you should evaluate your aggro rotation and your group make-up. As for attack duration, they are nice for DPS spec, and I use them religiously for all my characters dps builds. Tanking, i use both the partial mit rune and gem on both LI's because I find it much more beneficial to mitigate more damage on partial avoided attacks, (my total partials account from anywhere between 12% to 18% of my total avoidance when logged with CA.) rather than mitigate 1 to 2% more on rare crits (I don't get crit often considering our crit immunity proc)
Where has your Wadening taken you?