1)
When did Moshe make the rings of the Choshen?
2)
How did the Eifod hold the Choshen in place?
1.
Rashi and Rashbam: Via the two golden cords on top, which passed through the rings on the top edge of the Choshen and both ends of which were forced into the golden settings at the edge of the straps of the Efod; and via the Techeiles cords which tied the two rings at the bottom edge of the Choshen to the two equivalently-placed rings on the belt of the Efod.