Have him call his local pest control company. I know that here we can get a repellent that you can put down on the perimeter of your yard and snakes will not cross. I have never tried it because our yard is very large area - we mow apx 8 acreas. Anyway, maybe there is something that the pest control company can suggest. At least gardener snakes are not poisonous - but to me the only good snake is a dead snake!