Lock it from your device...
locking rotation of board

Even if you use the no flip thing, your device is going to auto rotate it's orientation. I would heed the advice of both the two prior answers and use the no flip option and switch off your auto rotate on your phone or tablet.

I can't find the no flip option. There's only new game, flip board and settings(which has best moves, threats etc.) Flip board changes the orientation for one move and it's back to flipping at every move after that. I want to be able to lay down my device and play with a friend.
How to lock rotation of the board when two players are playing on the same device?