I think that once they can roll freely you can't really stop them from sleeping on their tummies.
This is what happened with my DD. Once she could roll, she preferred being on her tummy & if I flipped her back she'd just wak up or roll back to her tummy again. By that stage she was in a sleeping bag and she used to move about her cot alot, so not much I could do about it.

I'd just follow all the other SIDS guidelines - make sure mattress is firm, not too hot in the room etc...