I was told the same as Melanie, once they roll on your own there is nothing you can do about it. You could buy a device that holds them flat, but there isn't much more you can do. I was in a sleep school with Matilda when she was 10 weeks old and she started rolling at that time (we were there to try & get her to sleep on her back as she refused too) and they told me that was it, she'd won the battle & there was nothing else I could do but start settling her on her side or belly.