I use #10 cotton untreated canvas duck. It shrinks nicely. Yes, nicely.
Staple it under the table top edge/board. Don't worry about "how tight."
Then, just get some hot water and sponge it to soak the canvas.
It shrinks up like blue jeans... and does not loosen with use.
Here' a photo of my wedging table. I also have two large work tables also covered with cotton duck.
It lasts for years, and mine seem to stay tight forever...