just a word to the wise.
I would not mount the D-rings to ride in a semi-permanent position. Why? First of all if you tighten the pins tightly enough to keep from vibrating loose and falling off. You will find yourself running around trying to find something to remove the pin to put the D-ring through the loop. Never a good thing to do at all the wrong times.
What I do is keep my D-rings along with my straps in the wet-box up top of my X. Instantly accessed and ready to install on my front bumper (If I don't use my winch). As Danny mentioned this is where my hook comes into play on the rear. I have found that the hook provides an instant attachment for the strap on the rear of my rig. On other great side benefit, as Erik mentioned, it is a great guard for the spare tire and bumper on serious departure angle situations. That hook will take a lot of abuse that before those rocks ever get to the bumper or spare.
A little picture to show that a hook is very valuable in split second situations:
Do we have any opinions on D-ring tow hitches?