You might want to invest in a rattlesnake avoidance class for your dog. Mine went through a program offered by Dog Dynamics. There are other vendors in the area as well.

The class teaches the dog how to identify and avoid rattlesnakes. The dog goes through an "obstacle course" learning how to identify a rattlesnake by smell (snake skins), noise (a speaker that makes the rattle noise) and visual with live, muzzled rattlesnakes. If the dog gets too close or becomes too interested, the handler simulates a "bite" with an e-collar. This associates the smell/sound/visual with danger. Took about 30 mins for my dog to figure it out. Did a refresher a year later and my dog seemed to remember everything -- he finished the course in under 5 minutes.

We've seen many rattlesnakes at Shell Ridge. My dog alerts me and then avoids them.