http://www.texas-venomous.com/myths.html
MYTH: If you are sleeping outside on the ground at night, place a rope around your bedroll because snakes will not cross a rope. Another varation of this myth is that snakes will not cross a railroad track, so many of the illegal aliens crossing into the U.S. on foot frequently sleep on the railroad tracks to keep the snakes away.
TRUTH: Snakes will in fact cross a rope on the ground. They will also cross railroad tracks. Unfortunately, many of those people who sought safety from snakes by sleeping on the railroad have met with a much more deadly danger than the snakes that they feared.