Probably can't stop it completely, but oiling will help a lot. Also, storing in an air conditioned environment is not good, and will accelerate drying. Best to store it in an air tight container if really concerned. If one lives in a very dry region, there is not much that can be done other than to oil it often. Ivory is as bad or worse. With either, in making grips, it is best to let the blanks sit a month or so before using. Especially if you have cut the blanks from a larger piece. I one time left a half dozen knives in an air conditioned store, on consignment, and after a few months found that, believe it or not, even Westinghouse Micarta had shrunk noticeably. I had to re-finish the tang edges to level them down again.