For years, and I mean years, I've pinned my quilting to carpet. Never used duct tape. Pin the backing (wrong side up) across one end (squared up to the wall) and place the pins in at an angle with the heads over the carpet not the quilt. Pin the opposite side, then do one side and finally, the last side. The backing should now be pinned to the carpet under SLIGHT tension. Float the batt down, centering it on the backing. Do NOT pin the batting. Finally float the top over the batt (right side up), centering it. Remove one pin at a time and place into the top. Pin in the same manner as the backing. When all done, you should have the quilt sandwich pinned to the carpet under slight tension. Starting at a narrow edge, remove one pin at a time and begin basting. I baste in serpentine rows about 4-inches apart. Use a basting thread that removes easily (Coats & Clark has one) called Basting Thread (duhh). Continue the rows of basting removing the pins as you progress up the quilt and rolling the quilt as you go. When all done, the pins are gone and the quilt sandwich is ready to quilt. Never had any shifting with this method, nor has the backing rippled. I've done both hand and machine quilting using this method. Good luck.
SandyQuilter