Make unit invulnerable

How do i make unit invulnerable ?
Ive looked trough the whole units, uhm how do I put my words? abilities?
Anyway..
I feel so dumb.. :(
I thought that was an easy thing to do..
but.. no.. :P
anyway? I must have overseen something! ;P

if your that new, i have to tell u
go to the unit's abilities in object editor and add (neutral) invulnerable