All you need is:
- Pencil (or chalk)
Cut out what you drew on the leather (not necessarily a triangle or a rectangle, use your creativity); glue it onto the paper, cut the leftover off and it is ready ! You don't actually need to glue the leather onto the the paper but if you want something harder I advice you do.
Here is a solution for those who don't have any page marker as well as myself. Never lose the page you were reading!