Triggering help

Triggering help

I need a trigger so that when the game starts you can see something but then when you do something you cant...

This is the trigger i am using now:

Event - A unit enters playable map area

Condition - Owner of last created unit equal to player 1 red

Action - Disable last created visiblity modifier

what is wrong with that if there is anything??

1. If the event is unit Enters wouldnt the condition be entering unit?
2. WHen was the visblility modifier created? If never then Last Created Modifier region wouldnt work.