Use backface culling then you can visually see if the face normals are pointing the right way. In the viewport click > rendered menu at the top > high quality render click the box to the right, this will show a pop up window - check occlusion culling and make sure the drop down says single sided. Picture here
This way you can always see when normals are facing the wrong way. If they are you can use the flip normals in the normals menu under polygon section (highlight the faces, hold shift and hold RMB to then go to the face normals menu then Reverse Normals.