I, too, just purchased a house with a large, sloping yard. My problem is not as severe as yours, but half the yard has a 45 degree slope down to the driveway which makes it hazardous for family use. Come this spring, I will be terracing that part of the yard (which faces east) using either timbers of some sort or flagstone and making steps and flower beds. It will be a big job, but will certainly be worth it. Might want to try something like that for parts of your yard. Good luck.