Help with setting directions?

I'm teaching a game design class and one of my students is making something like portal. He's got the shooting portals and moving through them thing down, but he's having trouble getting portals on a horizontal surface to be horizontal and similarly with vertical surfaces. Whenever the "portal bullet" hits one of the walls it just displays its horizontal mode. I tried making the creation of the portal set direction relative to the ball that was launched but that didn't quite work. Anyone have a simple solution that I'm not seeing?

I think you'd be best of referring to the direction as a number, and then inverting it when it collides with something. In this case, if you're only going for horizontal and verticlar, a simple event like "Direction of portal is right, portal is colliding with backdrop, set portal direction to left", and perhaps having some toggle-value that goes from 1 to 0 when it collides to avoid it flipping back and forth between direction.

How's that?