Organic Frog

What is the easiest way to dig up dirt for a water garden?
I have been digging a hole in my yard for a water garden that I am going to construct, but the soil is rock hard and in-organic and because of the hole's location in between two huge trees there are thousands of roots from small grass roots to huge 6" thick or bigger roots from the trees. I've been using a hoe to loosen the dirt for shoveling and to cut the roots, but it's becoming an extreme physically enduring project. Are there any other low-budget methods to get a hole dug? Remember, I need to dig a hole to match my measurements and designs for a water garden, not just a big hole.
Note: A water garden, in my case, is a small man-made pond with fish, aquatic plants, frogs, etc.
Either rent , or have some one come in with a machine called a
Bobcat .Its a very small bucket loader , that will do the job in minutes ..I use one all the time in my line of work ( landscape design )
Here's a link to view one ...
http://www.bobcat.com/worksaver/99bc/ws_99bc_loaders_453_01.html