Knut Erik, I think your method would work. Mine was only an alternative.
As an additional point, I'd make the trigger type switch. Have the guard on a HOLD waypoint and synchro the trigger to the waypoint. The guard's next waypoint should be SEEK & DESTROY. Put it right next to the hostages. That way, if anything goes wrong with the commands, the guard is in the right place doing the right thing. You'll need to give him other waypoints after the S&K, (maybe CYCLE) otherwise he'll eventually just stand there.