Jill, for years I've had to use bungees to keep really large plants and pots from going over and off benches. When you have huge Alocasias in 20 gallon pots, they are not something you want to have to stand up after a storm. I had to use industrial strength heavy rubber or polyurethane bungee cords in quantity to do the trick, but they worked. That is, until the plant got too large and I had to move it up to an even larger pot!
Note - if you find occasion to need heavy bungee cords for outdoor use and don't want to wake up one morning to find your cheap bungee snapped and left your pot full of plants to crash to the ground, look into "perfect bungees". They are made from polyurethane, not rubber, and do not deteriorate like the rubber ones do. I've had black rubber bungees that appeared to be in perfect shape, yet they suddenly snap in two without warning and the plant goes flying! Perfect bungees won't do that to you - besides, they come in really exciting colors, not just black! I like the hot pink, purple, fluorescent orange and red, but the other colors are great, too. Google "perfect bungee" at amazon.com to see them.