All possible snake entry places should be blocked. Galvanized screen can be used to cover drains or ventilators. Insulation can be used in cement cracks or where pipes go through outside walls. Vegetation should be kept short around the buildings. Mowed lawns and short cropped fields near the house are less attractive to snakes and the rodents they feed on.
Snakes like to hide under objects.
This maintenance will also discourage the presence of rodents and other animals such as skunks.