Not sure a nine game schedule works with the ND alignment. But if it did happen, the best way to do it is to have one permanent rival for the ones who make sense, and alternate the rest. No need to force rivalries. This was the ones that have one, play the same six teams in their division and one cross division team every year, and the other six teams every three years. The ones that don't have a pigeonholed cross division opponent, can play most teams an average of every other year, playing each team 3 times per seven year cycle.