Simple Shackle Macro
WoW Priest Macro
This macro will allow you to set a target as your shackle target then cast it upon them whenever you hit the button, no matter who your current target is. Can be spammed without interrupting itself due to the way the /stopcasting command is written. Hitting the Shift button will also force a Focus shift to your current target (can be modified to either ctrl or alt if you so choose, or even replace it with button:2 to refocus on a right-click).
/stopcasting [nochanneling:Shackle] /cast [target=focus,exists,nodead,nomodifier:shift] Shackle Undead /stopmacro [target=focus,exists,nodead,nomodifier:shift] /focus