Are you talking about piecing or quilting. If you are piecing, there really isn't any need to secure stitches because the stitch gets locked when you sew your unit to the next piece. When joining rows of blocks your stitch gets locked in when attaching a border, or the binding in the case of non bordered quilts. If you are truly concerned about your units coming apart you can take a backstitch or simply reduce your stitch length for the first few stitches. Same goes for quilting. You can reduce your stitch length or you can knot and bury your stitches.