If you will be hemming or cutting your fabric and don't need fringe, use a "tail" of your weft yarn, a little longer than the width of the warp, to quickly overcast the edge. Take long stitches zigzagging in and out of the edge of the fabric. There's no need to count threads or rows; the purpose is just to stabilize the edge until you can secure it off the loom. While I do it on both ends, this is most important for the final edge of the fabric, which can ravel quickly.