I guess you should hide behind your golf bag? Protect the eyes, the head from all positions, and genitals (ouch wouldn't want to get hit there by a golf ball!!!!)
I remember we were taught in the army to
-lie on your stomach
-keep your legs together, soldier's fat buttocks and thighs are guarding the family jewels
-put your face in the dirt
-and put your hands behind your neck.
That's in case of enemy artillery attack! I suppose it might protect a little bit against shrapnel, but you never really know, do you? A soldier would have shrapnel protecting vest, front and back. Together with helmet, protecting the head. Soldier's fatty legs and butt protecting the genitals. And hands protecting the neck.
I suspect that the optimal safety position, in open terrain vs golf balls
-sitting position, back towards the danger, genitals are protected
-tuck in your head near your chest.
-try to protect your neck AND the top of your head, with your forearms
Golf ball might still hit you in the kidneys or something, which would be the worst case I suppose? But would it really do damage though? You couldn't reasonably protect your back in this sort of case study (open terrain, somebody yells fore)