Do the chemicals you see advertised in gardening magazines claiming they will keep snakes out of your yard really work?
Don't know re sulfur and am not a pro, but have had copperheads in and around our yard. Black snakes are not poisonous and keep copperheads at bay. Snakes know you are there by vibrations and that can warn them. You need also to know if you're dealing with pit vipers (poisonous: have a pit between the eyes) and non poisonous snakes. If the former, try .22 caliber bird shot from a distance if nothing else works. If the latter, they may be beneficial: keeping down rodent and insect population and not harming you. Some country folk consider having a non poisonous snake (garden snake or black snake for example) living around your house to be a good luck. Bottom line: call County Agent for more specific advice and give the pit vipers a wide berth.
Do we know this is an American query? To discourage snakes, clear away long grass and any unnecessary timber, sheets of tin garden pots, etc. This means you and the snake will see each other along way off and avoid each other and snakes don't like to feel exposed unless sunbaking. ALWAYS put a shallow container of water outside your yard, if on a property, or in your least visited corner, so that if it comes in thirsty, it needn't come near you. Snakes LOVE a feed of mice, so try to get rid of them and make sure your pets can't get at the poison, if you use it. Honestly, unless you have a feisty Jack Russell, both you and the snake just want to live quietly. I've accidentally put my foot down, literally next to a curled up brown snake, poisonous and bad tempered, and automatically apologised as I stepped back, (upbringing). I have 2 brown snakes in my backyard. They keep to themselves, hunt my mice and we endeavour to live, happily ignoring each other. I know where they live and neither of us would dream of visiting without being invited. We share this world. We don't own it.