You can get a magnetic seam guide at Hancock's that is "thick" enough to keep your fabric from shifting over it. It is better than using a post it note, or tape or moleskin. Of course your machine base would have to be metal for the magnetic guide to hold. I have only seen them at Hancock's, but you might find them in other fabric shops.
http://www.hancockfabrics.com/Magnet...VVviewprod.htm