Just wanted to share this macro for the DK's out there that want to help their raid out with Twilight Sappers in the Dragon Soul raid (blackhorn boss):
#showtooltip Death Grip
/tar Twilight Sapper
/cast [@target,exists] Death Grip
/cast [@target,exists] Chains of Ice
This will basically put your current target on focus, target the sapper and apply Death Grip + Chains of Ice and then return to your focus target (that you were dps'ing / tanking before going after the sapper).