An easy way to get more years out of your players for the same salary is to simply injure them. When a player is injured his stats are temporarily decreased. While he is injured go and negotiate a new contract with him. You can usually get them to commit to 7 seasons for the same salary they already have or for even less money. This can be done any time during the season when the player you want to negotiate is injured. Note: Doesn't work when the players end up retiring.