WoWInterface - Non Interruptible spell cast on target castbar

So got a request to add a non interruptable shield or notification to my target cast bar in BobUI, what would be the best way to go about this? Currently I really just use the deault castbars and modify it like so

Lua Code:

--Target Castbar
local tbf = "TargetFrameSpellBar"
_G[tbf]:SetSize(cfg.targetwidth,cfg.targetheight)
_G[tbf.."Border"]:SetSize(240,40)
_G[tbf.."Border"]:SetPoint("TOP", _G[tbf], 0, 15)
_G[tbf.."Border"]:SetTexture(nil)
 
_G[tbf.."Flash"]:SetSize(240,40)
_G[tbf.."Flash"]:SetPoint("TOP", _G[tbf], 0, 15)
_G[tbf.."Flash"]:SetTexture(nil)
    
_G[tbf]:SetScale("1")
    
_G[tbf.."Text"]:SetPoint("BOTTOM", _G[tbf], 0, -2)
_G[tbf.."Text"]:SetFont(cfg.font, cfg.targettextsize, cfg.style)
 
_G[tbf]:SetStatusBarTexture(cfg.statusbar_texture)
TargetFrameSpellBar.showShield = false;
_G[tbf]:ClearAllPoints()
_G[tbf]:SetPoint(unpack(cfg.tbf_position))
_G[tbf].SetPoint = function() end
 
_G[tbf.."Icon"]:Hide()

when i was originally working on it I had difficulties finding the image file for the non interruptible frame so I could just change the texture to a little shield or something so I gave up and killed it off on line 18

anybody know the image path for it? I can't find it for the life of me....