On the attacked unit you can put a damage response (on a buff behavior). there is a little box in there somewhere that says "defender" and you will need to set that to "attacker". Put this behavior on the unit with thorns. Set the chance (at the top) to 1. Now, 100% of the time a unit with that buff is struck; something will happen to the attacker. It is early and I forget how I did the damage apply part; brain farting, and I gotta go in a min. bzzz...bzzz...bzzzz... If you don't get help elsewhere by the time I return from work in... 15 hours... I will post how I did the damage apply part. Someone else should have the rest by then though.