Plan your bog. Getting all your information from one source is a bad idea. Everyone has a different idea about making a bog garden. You can find many diagrams for bog gardens online and it is a good idea to look at them all. Taking ideas from a lot of sources will help you in making choices such as "How deep?" and "Where?". Speaking of "Where?" be sure not to locate the bog in a low area of your yard. By placing extremely water-retentive soil in a wet spot your bog garden will suffer whenever it rains and your plants will be submerged. Even flat bogs can fill with water. I found three especially helpful pieces on the subject at Meadowview Biological Research Station, at Botanique Nursery, and the Savage Garden. My own bog is dug to a depth of 14 inches and is approximately 50 cubic feet with sheer sides and a flat bottom. My bog was a roughly ovoid shape but could have been dug really as any pleasing shape. A good way to plan your bog is to lay it out with a garden hose, then dig the perimeter. Remove the garden hose and start digging down.