I had this theory to unlock the secret stadium. Maybe if you play an exhibition match at every stadium in the game you unlock it...so you go ANZ, then each one in sequence.
I found a cool way to cheat the sin bin. Just as you hit the high tackle, if Vossy says the players name or you think you kow who he is, interchange him immediately. He'll go off the field and get replaced. If you're not exactly sure, put on four players off the bench for who you think it may be. Then if you want em back on, put em back on again.