[allied] units un-attackable?

[2Clever4u]

Hey, i've been experimenting with editor for a week or so and im wondering how i would make a unit unable to be attacked by an ally. For example in rpgs where you cant attack your fellow allies. And no im not trying to make them invulnerable. Or if you could point me out to a object editor guide that would answer my questions thatd be great too

 

[scorpion182]

make it via trigger

 

[2Clever4u]

thank you!