It's really not too difficult. Just wait till they turn around and run behind them and do a melee. Now they are dead. If you set off the alarm, they are NEVER GOING TO STOP COMING. You aren't supposed to set off the alarm, so the game punishes you for it.
If nothing else, set off the alarm and then just haul ass to the checkpoint, cause once you pass the checkpoint it resets as if nothing was ever wrong.
You can't try to mash a square into a triangle and then complain cause it doesn't fit. Just get a triangular piece. Aka, the game is straight up telling you to do it a certain way, so do it that way.