Help with axle lock ring

[76m2002]

I've just replace a half-shaft on our '91 318is.  Got the car on the ground, axle bolt torqued, and I'm stumped about installing the lock ring.  What is the secret method of hammering the ring into the depressions without pulling the opposite side free?  I've managed to get the ring hammered into two of the three depressions, but it always pulls free when I go for the third.

[bmwman91]

I used a socket, forget the size. Put the open end on the lock ring & hammer it in with that!