You can either handle this with hitTest (if hitTest is true, dont allow movement there) or use a tile system to detect impassible portions of a gridded map. Instead of hitTest, a grid position is crossreferenced with the grid position in a lookup table which contains the valid and invalid positions of movement. If valid, move the clip, otherwise dont.
your best bet is to check around for downloadable examples. There are plenty floating around out there. (though maze examples may not be quite so abundant)