Editing WoW:Useful macros (old) (section)

=== Acquire focus target / toggle between previous target ===
 /clearfocus [modifier:ctrl]
 /targetlasttarget [modifier:shift]
 /stopmacro [target=target, dead]/[modifier:shift]
 /focus [target=focus, noexists]/[target=focus, dead]
 /stopmacro [modifier:ctrl]
 /target focus

How to use: If no target=does nothing. If you have a target but no focus target, it makes target focus target. Once focus target is acquired and current target is anything but focus target= switches active target focus target. Hold down Control + activate = replaces focus target with current target (or clears if no current target). Hold down shift + activate = toggles between current target & last target.

Replace either ctrl or shift with alt if that modifier key works better for you. Also, it will not let you add a focus target that is dead. If you want to focus corpses just delete the "[target=target, dead]/" from line 3 and "/[target=focus, dead]" from line 4.