You know, my husband mastered the back kick faster than anybody else I'd seen, and this is how he did it: He went to the local pool in a bathing suit -- no fins. He floated on the surface and played around until he started to go backwards. He kept at it until he could swim laps backwards. Then he added fins (still on the surface, no gear) and played with it until he could swim laps backwards with the fins. Then he put on scuba gear and presto! Back kick. You could try that.