Melbourne centre-half-back Jared Rivers believes AFL defenders will be forced to play entirely differently in 2007 in order to cope with the league's much tougher push in the back interpretation this season.Rivers, one of the AFL's best defenders and the winner of the 2004 NAB AFL Rising Star award, said the new rules had forced his entire mindset to change ahead of the start of the pre-season NAB Cup this weekend.While for years defenders have been able to get away with minor pushes on opponents in marking contests, this year defenders will be penalised even if they just place their hands in the back of an opponent.And with Melbourne's NAB Cup game against Hawthorn on Sunday at Telstra Dome being the chosen game for an AFL experiment in which all nine officiating umpires can pay free kicks - rather than just the four field umpires - Rivers is anticipating a tough day at the office."It's going to be quite interesting and hopefully down back they will take it easy on us," he said of the possibility of even goal umpires paying a free kick against a defender for a minor push.When asked if he would have to play differently not just on Sunday but all season because of the AFL's rule changes; he replied; 'Absolutely'."All your life you have been using your hands as much as you can so it's going to be quite different," he said of the tougher in the back interpretation in marking contests."I am not sure (if the change is good for the game) and it will be a lot harder on people definitely but they are the rules and you have got to get used to it."Rivers said he has been working hard at training to come up with alternate means of spoiling without giving away a free kick."With one-on-one marking you've got to try and move your body more and push your body into them instead of using your hands because in a couple of the practice matches if you put your hands on the back it was bang (a whistle for a free kick) straight away.""It is difficult but these are the rules now so just have to work to your strengths and try to do the best you can to punch the ball away without holding on or pushing."But while Rivers is predicting a tough season for the game's defenders, he is optimistic about Melbourne's chances not just in the NAB Cup but more importantly for the season proper.The Demons have reached the finals the past three years and Rivers believes the club's 'window of opportunity' to win a premiership is now well and truly open."Definitely," he said. "Our playing group is really looking forward to the next couple of years, as a group we have got high expectations and hopefully we can follow through on them."