If your DF is worried about rolling on bubs you could ask him to think about when the last time he fell out of bed was or the last time he rolled on the cat (if you have a bed hogging cat like mine). The same senses that stop you from rolling out of bed will stop you from rolling on your baby. Amazingly enough all our senses except smell still work while we're asleep and although we're not conscious of it we can make descions in our sleep that safeguard ourselves and others.
Also if you sleep in the recovery position it's very difficult to roll.