The DCR has a publication here on the preservation of stone walls, with lots of references to good historical and legal resources. They write:
How do we learn to recognize these features when toppled stone boundary markers or collapsed and tree-filled cellar holes often go unnoticed in the woods? Even when identified, it may be assumed that their isolation removes any relevance or historic significance. But it is exactly these types of landscape elements that tie the land to a past use and history that may no longer be immediately discernable, and without the skills needed to identify these features their eventual loss is assured. However, stone features can be protected through proper stewardship that addresses threats such as neglect, collapse, and damage from vegetation and theft.
Deborah Howe
Toby Wolf
Have you read “Stone by Stone” by Robert Thorson of UConn? That should also lead to more good material on stone walls.
Stone wall theft is a terrible thing. A friend who was moved to a nursing home had her complete stone retaining wall removed: a shock. Her house was on a back road in Knox County, Maine.