How do I convince my husband to restore his foreskin?

You might just consider minding your own business and not belittling your husband by inferring you think he is inadequate or strange. Being circised was not his decision, and how he appears is no fault of his own. But if you have had him as a husband and lover for this long, why in the world would you bring such an idea up unless you have other issues and are just using this to create discontent in your marriage. His , his business, not yours even as your wife.