Without getting into the question of the walls of a canvas sukkah (see Shulchan Aruch OC 630:10), what are some easy and practical methods of making kosher walls in such a canvas sukkah? (We try the string method every year and it doesn't work out too well for us on many levels...)
I used to use string, but I graduated to using mailing tape between the upright poles. After I build the frame and before I add the canvas, I put mailing tape around the outside of the sukkah in place of strings (with the sticky side facing in). For practical reasons, I also put a second layer of tape on the inside over the first one so that things don't get stuck on the tape.
The tape holds its integrity over Sukkos, and doesn't slip. It also can help with wind blowing the canvas. The whole thing takes less than ten minutes, and the tape is cheap at the post office.