Cannot create shortcut for show/hide Dock (Cmd-Option-D)


How do I set up a key sequence to invoke showing/hiding of the Dock on my Mac? I can't seem to find show/hide Dock under Predefined actions and when I try to enter the keyboard shortcut under "Trigger Other Keyboard Shortcut", the dock actually shows / hides and no key sequences show up in the Trigger Other Shortcut field.