The dogs are not accustomed to interacting with snakes, either as something to be avoided or as prey. It doesn't smell like a rodent. More importantly, it doesn't move like a rodent. It does not have a neck, at least not in the same fashion that a rodent has a neck. In the video below you can see how perplexed the dogs are, well, except for Stoic.
I rescued it from the dogs on two occasions but it kept on moving toward the house, and Stoic kept on finding it. I am sorry to report that he did eventually kill it, still, little snake, I did all I could.