Ya, you gota think something is attracting them to your root zone especially this time of the year (plenty for the critters to eat). Root zone critters are hard yet easy to stop. Using liquid fence probably won't work, but watering heavily to work out what ever is attracting them may work. Problem with heavy watering is plants are not always in a prime location to water heavily. You can also put up wire fencing, just dig down about 12 inches. Also, growing in the corn has one real major draw back, farmers need pesticides that work so most of them are petro chemical, and are very bad for smoking, their fertz are also pretty bad as well, so be careful.