Turtleskin chaps
https://kevinscatalog.com/turtleskin-total-chaps-regularGoogle will give you several sources. They are expensive but not nearly as expensive as medical treatment for rattlesnake bites. I don't like to wear leggings or chaps when hunting, but certain places and times of the year I do. I haven't personally tested them against a rattlesnake bite, but one of my regular hunting buddies has. They work.
Turtleskins makes half-leg (below the knee) protection chaps, full leg protection chaps, and gaiters.
The Filson chaps are great and wear forever, but even their double-tin chaps are not snake proof.