I've kept Moleskine 365 Day diaries going every day for over 10 years. Never missed a day. I've tried dozens of pens and methods for keeping them handy. I found a pen called, "lePen" that is very thin, has extremely dark ink and does not bleed through the page (also very important). It's small enough to simply clip on the spine. No alteration needed! I have to replace the pen every couple of months, but they are pretty inexpensive. I like a fresh new tip every now and then anyway.