I think the real resistance to natural law ideas today is grounded in the deeper resistance to belief in God. Would you agree? So how can one ever convince the skeptic of the natural law without first convincing him that God exists? If he is sophisticated enough, he'll point to all the objections you make in your work to non-theistic conceptions of natural law, and say that neither God nor natural law is real. We have to buy the whole package or nothing at all, don't we?
And, from a pedagogical point of view, how is a teacher to persuade religious skeptics of the existence of the natural law without “coming clean” that you do have to buy the whole package?
Yes, I've given a lot of thought to this problem. A lot a thinkers try to motivate the discussion of natural law without mentioning God. If they find it helpful, why not? But I think they must have a certain kind of skeptic in mind rather than skeptics in general, and I can't help noticing that conversations which begin by avoiding the mention of God don’t usually go on that way.
My own approach is to start where the skeptic is already -- wherever that may be. I don't hide the fact that I think an adequate account of natural law requires belief in God, and when I'm teaching, I don't hide the fact that the mainstream of the tradition has taken that view too. But unless there is special reason to do so, I don't open the conversation with a skeptic by saying "Premise one. There is a God." God will make His own appearance in the conversation.
There isn’t any way to know ahead of time how such conversations will work out. Some atheists come to believe in natural law, then think "But then there must be a God!" Good.
Other skeptics come to believe in God, then think "I must have been wrong to think there is no natural law!" Good.
Still others are tempted to believe in natural law, then think "But that can't be right, because then there would have to be a God!" Okay, then we talk about God.
There are even some who come to believe in natural law, but insist that they can make natural law theory work without God. This in turn induces errors in their conception of natural law itself. In that sort of conversation, the most helpful place to begin is usually to demonstrate the errors. Eventually God comes into that conversation too, but I try not to jump the gun.