Then all you need to do is cover them with paper. You do need to keep it flat and not too many layers of paper. One tip though, you might want to put something on one side that tells you its that side of the bookmark you were reading. Of course if you are using them in cookbooks or other reference books, I use them in my German course book, you might not need to know that.
Here are some I have made using different Craft Consortium papers