Take a 1 x 4 about 12 inches long. Pick up some six-inch nails and pound them through about three inches apart. Once the ladder is in place, push the 1 x 4s against each leg stabbing those spikes into the grass/soil. That will add extra protection from those rubber feet sliding on the grass. The rubber feet are really only effective on a sidewalk or driveway. On grass -- well, slide a wet gym shoe against grass, and you'll get the picture.
I used to just stick a large screw driver into the ground against each leg, till I got older and a little wiser. All it took was about a three inch side motion from those legs to make the screw drivers ineffective. -- Sonny Lykos, on The Old House Web Bulletin Boards.
