I've been taking small (or in place-called a lockstitch) stitches to start/stop machine quilting for years- bring the bobbin thread to the top- hold both threads, take a few tiny in place stitches, then continue on - then when I stop for what ever reason I go ahead and cut those two threads at the quilt surface. the quilting is never the issue if a quilt comes back for any repairs. I've never had the quilting come undone. 3-5 stitches are enough to lock your stitching- then you set your stitch length where you want it & continue on- I also run a line of stitching around the outer edge of my quilt top (if it has blocks/seams along the outer edge-not just a straight border) to keep the seams along the edges from pulling apart. when a seam is crossed it is secure.