If I was running 3 locks behind my pally, I'd spec all three Meta/Ruin. I'm not sure the diversification of specs is worth the loss in efficiency. Maxxing an affy lock requires very timely dot refreshes. That's hard to do while you're mashing your shadowbolt button on the meta/ruin lock. Finally, the beauty of the felguard is the constant, low-micro "dot" that it provides. Just sic him on your target while your pally's taunting and he'll never pull aggro and yet be a constant stream of DPS. Top that off with three locks pounding shadowbolts and stuff will drop in a hurry.