How old is DS?
When dd started rolling in her crib, instead of trying to keep her on her back by rolling her back or using bumpers, we comforted her when she rolled. That way, she wouldn't be afraid of the tummy sleeping...since we figured it would have to happen eventually. We did pat/shh when she rolled over and pu/pd if necessary. But every time she woke crying we just shh'd her back to sleep on her tummy. And we may be lucky, but it only took one night and about 3-4 wakes for it to be done.
Good luck!