The following recipe is designed to create a slightly distasteful (to pests) coating on plants. This spray will last in light rain, but should be reapplied every 2 weeks or after heavy rains.
Combine the following in an empty gallon jug:
1 egg, beaten
1/2 cup milk
1 Tablespoon of cooking oil
1 Tablespoon of dish soap
Fill the the jug with water, cap and shake well. Spray or sprinkle on plants.