1. Put a large clear plastic dome over your house.
2. Get out your shotgun every time you go to the back yard and shoot down the incoming golf balls. (After you do this a few times, I guarantee that the odds of you getting hit will go down tremendously.)
3. Make sure that the wife has a big martini ready for you when you get home. This will not improve the odds against you getting hit but it will make you feel better about venturing into your dangerous back yard.
4. Provide helmets for you and your guests when they venture into your dangerous back yard.
I guess that you could put up telephone poles and string chicken wire between them but that might be pretty unsightly.
Come to think of it, the best answer might be for you to move to Colorado. The scenery is even better but then how do you feel about avalanches?