I think beneficial nematodes may help a lot with this problem. They interrupt the soil stage for many pests (fleas, moth/cutworm/vine borers, beetles, and more). You'll need to apply them in a cool time of day after a substantial rain or a very good watering, and put them out at dusk so they're not killed by sunlight before they get into the soil.
You can order them online if you don't have stores locally that carry them. This is one place that carries nematodes and many other biological solutions to pest problems. They often do a spot on the weekly radio program.
Arbico Organics
P.O. Box 8910
Tucson, AZ 85738-0910
1-800-827-2847
info@arbico.comhttp://www.arbico-organics.com"Comprehensive pest control solutions. Beneficial Insects, Natural Fly Control, Mosquito Control, Organic Pest Control, Beneficial Nematodes, Grub & Beetle Control, Insect Traps Farms & Gardens."