ok if your going to use an all mage team then i suggest using a /assist macro instead of focus cause then you can use the following macro for your focus

#showtooltip
/clearfocus [target=focus,dead]
/focus [target=focus,noexists]
/script SetRaidTarget("focus", 1)
/cast [target=focus]Polymorph
/stopmacro [nogroup]
/s --== Sheeping and Marking "%t" ==--

Which does the following

  1. Clear your focus if your old focus target is dead
  2. Clear your focus if your old focus target doesn't exist anymore
  3. Set your focus on what you have targeted if you don't have a focus already
  4. Place a Star marker over the head of the focus target (if you are group/raid leader/assistant)
  5. Polymorph the Focus target
  6. Announce the sheeping.