My Grandparents owened a grain/feed mill. While in school I worked part time in the mill and farm store. We sold lots of things beyond grain; differnt minerals, salt blocks, fertilizer, feed additives, etc. One thing we sold a lot of in the Spring/Summer was Dusting Sulpher. If you are not familiar with it, its a florescent green/yellow color and has a strong supher smell. Typically its used a topical treatment in agriculture to keep bugs off crops...grapes and tree fruit a lot.
Anyway, several "old timers" would buy it in 50lb bags and circle their yards/homes because snakes won't cross it. They would reapply a couple times during the season and swore by it.
Maybe worth looking into.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)