Place 20% water and 80% glue in a small container (you don't need much of the mixture). Mix thoroughly. Place a piece of paper between the front cover and the pages (try not to glue the front cover to the pages) of your book. Apply to the edge of the book (while the book is closed) with an old paintbrush. Place 2 or 3 heavy things on top of your book while drying. Let dry for 50 minutes. Repeat once.
Open the book and make a line with your pencil that consistently runs 1/2 in. from the edge of the page. Repeat on all four edges.
Now for the fun part! Get out your X-acto knife and cut along the edge of the lines that you made earlier. DO NOT CUT YOURSELF!!. For your first few cuts, trace the X-acto along the edge of a ruler so your line is nice and straight. During this process change blades every so often. Make sure to get the corners, otherwise it will look awful raggedy. Cut until you reach the back cover. WARNING! Do not cut through the back cover. Glue the back cover to the pages. Liberally apply glue to the inside edge of the pages (inside the book). Let dry. Hide your valuables, electronics, bugs (listening devices, not the other kind), miniature spy cameras, or any assortment of spy equipment. There are endless possibilities! HAVE FUN!