I know this topic - about fencing laws - has been discussed in the past (few months) on NAT. Quite frankly, I don't really understand the logic behind some of these fencing laws.

I think there is value in talking with your state legislator about this situation, and seeing if there is value in updating the law to make it relevant. The whole idea of you needing to buy and install fencing so your neighbor can put cattle on his land seems absurd to me.  I would think that he should be responsible to keep his cattle on his land. At least that is the way it works here.