Worms can pop them out of the ground. Plant an inch deep in sets of 5-8 seeds per hill, in a hill about two feet across and a foot tall. I like to flatten out the top and plant them in a circle pattern. Until the seeds sprout, you want to keep the ground wet about an inch under the soil, because they need the water to germinate. To test if you need to water pre-germination, stick your pointer finger in the hill up to the first knuckle, if it's dry at the tip, water.
Once they're out of the ground, cut back watering to about once a week (will encourage deeper root growth), unless you get brown or limp leaves (sign of inadequate water).