Sense Undead WeakAura

Anyone know how to make a WA to show the icon for Sense Undead if (1, my current target is an attackable undead (player or NPC) and (2 I don't already have Sense Undead active?

I can't find the 'Target is undead' anywhere is triggers, and tracking spells are non considered auras thus can not be used for triggers that way, either.. I also can't just have it on at all times as I have herblore, thus I want to be using THAT instead and only using SU while in my ret off spec, with the glyph active and will be attacking undead.

Cant u just macro it on for example mount macro like
#showtooltip (mount name)
/cast !Sense Undead
/cast (mount name)

???
It can be any other spell
GL

But I want to be tracking herbs 97.6% of the time. I only want sense undead active while I have the glyph and will be fighting undead..