Don't know of any effective "snake replellants", my brother in NC, dog got nailed by a copperhead and was in the hospital for a few weeks, we didn't know if Misty was going to make it. My brother lives close to the Neuse river and in a heavily wooded area, so those slithery creeps crawl in an out of his yard and under his home. I searched several websites, and even park rangers and some of the vsarious universities, say the best one can do is not have bird feeders near the home/yard, the excess seed attracts mice and other rodents, which then attract the snakes.
When I lived in PA, huge (4-6ft) Black Rat snakes, would come around, and I had no birdfeeders but had some birdhouses scattered in the wooded area on my property, they'd slither through the wire fence attached on our post fence, sunbathe in the area my son had his playset and where my dog(s) were. You know, though they say they are non-venimous I still didn't want them near my home.
It petrifies me when I see anything other than a garter snake around, too many species to get close enough to determine, "venimous or non-venimous".
My brother's neighbors and the local hardware store said sprinkle sulphur (like used in gardens) along the fence, yeah, snakes still come in his yard, except Misty goes on the leash now.
Oh man, be careful, these critters kill, humans and animals.
Lots of luck with this.