I recommend the Clio waterproof pen liner.

I recommend the Clio Waterproof Pen Liner!

This is an item I've already been using for several days.

The price is reasonable, it applies well, and best of all, it doesn't smudge easily, so I'm really enjoying using it!

There are four colors available, but I only use the brown one. I like it because it looks much more natural than black!

(I just checked and it seems this product has been renewed as a Superproof Pen Liner! Only the case has changed, so it seems to be the same product. Please keep this in mind if you are planning to purchase it.)