Beware, alive command is treacherous, as units are alive or dead depending on the group leader knowledge. For example, you have a group of 8 units, the group splits in two or 4 each, one of the groups moves away of the other (where the leader is), and that group is suddenly destroyed by a bomb. Well, these units will be "alive" until the leader notices that his men are dead. This happens also with player's group, at some point to send a request status to some units and THEN, they dont reply, and THEN they are marked as dead and removed from your group. So, you better use damage _unit > 0.9.