I use lifelines and markers on lacy shawls, but they are not an end-all solution. I had finished a shawl and was blocking it, when one of my stitches was apparently missed (in a yarn over, I suspect.) There was a huge hole, even though I had used lifelines. To fix it, I reworked the ravelled part of the pattern, picking up the stitches and repairing up to a point. Then I used a needle and matching thread to finalize the repair. I have learned to "tug" on the lacy patterns every few rows, as well as using lifelines and markers.