I would explain the rattlesnake rules up front every time we go outside. At younger ages, if they broke a rattlesnake rule I'd pick them up and move them "I'm going to pick you up because snakes are dangerous."

Once they can reason (between 2 and 4 yo), instead of just moving them, I'd bring them inside and set them up with a different game, something still fun like legos, k'nex, tracing... as I did that I'd say "you weren't staying safe, so we're going to play a game I know you'll play safely." Kids also respond well to positive framings, so instead of saying "dont look under rocks" I'd say "next time, leave rocks be."

Is that helpful?