Why does the conmom slip up? Did he or you unroll it all the way down on his penis?? Was it loose when you put it one him?
Is his penis that small, that it rolls back up? If he has a large penis, then the regular condom should stay down at the base where it belongs. It may be tight on him but shouldn't ride up.
My guy is probably about average, 8 inches long and that much around as well and when he uses one, (regular size) it says in place.