On exterior walls, for outlets etc.  How is the romex fastened to the concrete within 12" of the box ?  Is foaming it in good enough ? The exits on the plastic boxes are right on the concrete.  What have you done that has been easy to do and passed code.

Thanks in advance

When I built my house I didn't. I cut the channels in the foam with a small electric chain saw so the grooves were just large enough for the romex. The cable had to be pushed to the bottom of the groove with a stick. The electrical inspector didn't have any problem at all with the way I did it. If there were two cables in one groove one was above the other.

If you are forced to physically fasten the romex the 12" distance applies if the box has clamps. Most plastic boxes don't so the distance is 8", not 12".