All AMs are off the GCD with the exception of DK. Maybe monk too, but I don't know the class well enough.
The problem is remembering to actually hit it every 7-10s, not I don't have a free GCD in time. Again, I'm more than willing to admit this is just a personal problem and I tunnel vision too easily. I've played prot warrior enough to acclimate to every other part of the class, I just find myself forgetting to hit shield block. Maybe it's not high impact enough, falling victim to the same problem focused rage does.
I think short cooldown abilities should be like frenzied regen where you use them reactively instead of maintain.
Can you actually maintain SoTR? I thought it had a 16s CD.
Monk AM is not off the GCD because you have to combo it with Blackout Combo for maximim effectiveness and you have to carefully maintain its charges. Once you get 30% haste maintaining Ironskin Brew isn't bad. But clearing dmg with Purifying Brew correctly makes the management pretty tight. Easy to remember because Special Delivery is procced off of it and that can be a good chunk of your dmg.