I am quilting a large quilt on the diagonal now, and 2 things that have worked for me are that "golfclub" thing that attaches to the walking foot and and moving a big sticky note along. Since I have to reposition every few inches, anyway, the sticky note works well (and I can pull it loose from the stitching when I accidentally mow over the edge of it.)
i did get the blue tape, but on my washed fabric, it seemed to be pulling a layer of fibers off when I repositioned it.
Hugs,
Charlitte