If you're not using a cheater needle already, check out this video by Leah Day:
http://freemotionquilting.blogspot.c...g-threads.html
Instead of sewing in place, I sew 3 to 5 teeny tiny stitches to start and stop. These stitches are maybe 2 to 3 mm long and don't create the "bump" that happens when the stitches are right on top of each other. These tiny stitches are very secure.