Protective Liner Stage
Make sure the weed or hardware cloth you use is large enough to cover the edges of the surrounding area. This is actually one of the most important aspects of bog construction. Voles in particular will not be able enter your bog a foot underground through hardware cloth. Work out all the bubbles and wrinkles, then spread 1-2 inches of sand evenly over the hardware cloth.
Most articles recommend at least an inch or two of sand on the bottom of your bog. This helps with drainage and provides cushioning for you main liner. Most often liners can be torn by small stones. The area that I dug in contained several nails being fill from my home's construction. As you can see in the photo I have placed rocks (and a shovel) on the edge of the weed cloth to keep it from falling in.

Design - Preliminary - Pest Liner - Water Liner - Padding - Fill - Mixing - Planting One - Planting Two - Finished - The Bog: Early Spring 2002 - The Bog: Summer 2002