Avator starts out with a good point, but I do not agree that the way to make the unit "miss" is by making it deal one damage to its original target. Instead, it is better to make it detect "whenever a unit is attacked" and make it create a dummy unit which casts a modified curse with 100% miss chance that casts it on the attacker. Since "Whenever a unit is attacked" event runs before damage is dealt, the unit will miss when it attacks.