I never back stitch. I teach my Learn to Quilt students to drop their stitch length to 1.9 or 2.0 as that prevents unraveling. On the outside edges if there is no border I use micro stitches to start and end seams. I use the "favorites" tool in my machine memory (Bernina feature, maybe some others too) to set a straight stitch at 18-20 stitches per inch, then I just do about 4 stitches to start or end a seam that I might worry about coming undone. Typically I do this on the seam that attaches the outer border since there are no cross seams. I've never had anything come undone on my quilts since I started doing this. One word of caution, however; it's impossible to unsew micro stitches.