I think I did this right, first time using Google Docs.
This is how to set up a one-time collision detection for any OPE-controlled player. Each side of the bounding box will detect collision with any solid object and disable control fro that direction. This way you don't have to worry about copying Area Detectors all over the place, unless I'm reading your example wrong
The Bounding Box instead accompanies the player throughout their travels leaving you, the creator, to construct your map without worry of leaving a hole open somewhere.

Of course if the player is controlled solely by OPE and there are stairs or inclines of any sort, that complicates things in which you should just be using Physics in the first place! But I'll go over that in another Doc.
https://docs.google.com/drawings/d/1...c_0/edit?pli=1
The 3D player model was found on the net and used without permission, but I hope it's ok here.
http://cghub.com/images/view/326278/