Applying masking fluid can be tricky. For precise control, I use an old-fashioned ruling pen. Designed for making even, controlled lines, the ruling pen was used by draftsmen, architects and commercial artists before the technical pen took its place. The nib holds a lot of fluid and by adjusting the screw knob, you can control the thickness of your lines. The ruling pen is the ideal tool for masking out fences, grass, power lines and many other fine details. After Im finished applying the masking fluid, I simply wipe off the pen with a tissue.