How do you repel black rat snake?

To discourage them from taking up residence on your property, start by eliminating their desired environments. Make sure your lawn is mowed and not overgrown with high weeds. Cut back overgrowth. Keep log piles and compost heaps a safe distance from your house. Use wire mesh fences at ground level around crawl spaces or your garden to keep snakes out of those places. Reducing the rodent population which is their main food supply will also send them elsewhere to eat. If you still find one slithering across your lawn, call the local Animal Control people to come remove it from your property.