Reverse Space Invaders Help

I'm making a reverse Space Invaders game where you control the aliens. To prevent the player from moving the aliens out of bounds, I tried the standard "alien leaves the play area, stop alien." However, that only stopped the aliens touching the edge of the screen. So I made Global Value A set to 1 when an alien tries to leave the play area, and all the aliens stop when Global Value A is 1. Global Value A is set to 0 all the time. The problem is that you hold down left or right, you can go past the boundaries.

Also, this is for a game jam, so I need a solution by tomorrow night. Help! :O

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With yours, the outermost aliens could escape for some reason. Weird.

Buuuuut, your use of overlapping and physically restricting the player's control led me to finding a method that works, so THANK YOU!