My Bernina also has a knot button that secures the threads. I'm getting much better at remembering to use it! Before I discovered it, I would set the stitch length to 0 and stitch a few stitches because I had read of this technique. However, I found that the 0 stitch length would come undone sometimes. Then I did the teeny-tiny (.03) stitches at beginning and end of a line of quilting. For extra security, I usually bury my thread ends, using the self-threading needle as yolajean suggests.