Arms warrior Power Auras Q.

[WarriorGuides]

Hey i recently went and i have yet to to find out how to see if my rend has "x amount of time left" through the use of an aura.
Just basically what do i set for the "Activation by:" for a debuff that the boss/target has on himself not me.

~Regards
EDIT: also feel free to add a need to know guide as im running both.

[lawomous]

Debuff on enemy target. This is the PowerAura I use, which only pops up as Rend has less than 5 seconds left, so I know when I need to reapply it, since it draws attention to it.

Version:st3.0.0E; gcd:bofalse; b:nu0.87843137254902; anim1:nu1; g:nu0.87843137254902; optunitn:bofalse; ignoremaj:botrue; stacksLower:nu0; target:botrue; icon:stInterface\Icons\Ability_Gouge; size:nu0.1499999910593; torsion:nu1; r:nu0.87843137254902; y:nu-76; x:nu1; customname:st; groupany:bofalse; isAlive:botrue; timerduration:nu0; unitn:stOnly for raid/group.; bufftype:nu2; stacks:nu0; focus:bofalse; raid:bofalse; texture:nu1; alpha:nu1; aurastext:st; symetrie:nu0; owntex:botrue; isResting:nu0; duration:nu0; mine:botrue; multiids:st; inVehicle:bofalse; speed:nu1; anim2:nu0; stacksOperator:st=; realaura:nu1; spec2:botrue; InactiveDueToState:botrue; threshold:nu50; exact:botrue; textaura:bofalse; sound:nu0; wowtex:bofalse; groupOrSelf:bofalse; customsound:st; combat:nu0; id:nu3; inParty:nu0; HideRequest:bofalse; Active:bofalse; aurastextfont:nu1; buffname:stRend; inRaid:nu0; tooltipCheck:st; customtex:bofalse; stance:nu10; isSecondary:bofalse; thresholdinvert:bofalse; spec1:botrue; Debug:bofalse; beginSpin:bofalse; Showing:bofalse; UseOldAnimations:bofalse; begin:nu0; off:bofalse; party:bofalse; texmode:nu2; inverse:bofalse; ismounted:bofalse; targetfriend:bofalse; randomcolor:bofalse; finish:nu1; timer.InvertAuraBelow:nu4.75; timer.dual:bofalse; timer.HideLeadingZeros:botrue; timer.h:nu1.5500000715256; timer.ShowOnAuraHide:bofalse; timer.UpdatePing:bofalse; timer.Texture:stDefault; timer.enabled:botrue; timer.Showing:bofalse; timer.lastShownLarge:nu34; timer.y:nu-68; timer.x:nu-1; timer.CustomDuration:nu0; timer.Transparent:botrue; timer.a:nu1; timer.HideRequest:botrue; timer.id:nu3; timer.cents:bofalse