OK, so this wasn't the beginning, but it was the beginning of the pictures. (excuse the large shadows!). I had at this point built the main frame with pressure treated 2x4's, to get the size, and started digging in the pond area. The 2x4's are at least 2 feet in the ground on the 'low' side of the lawn, and deeper on the higher. The entire frame is 'anchored' to the block wall, the top of which is intended to be a large, long sunning deck for the iguanas when this is done. It is high enough on top of the wall to see out front, back, and into the pool. The cage is basically L shaped, with one side being (mostly) pond, along the screen of the pool deck (about 11 feet), and the other side of the L going along the block wall that separates the back yard from the front (about 9 feet). This provided at least one real solid wall that I didn't have to build, and no one would get in or out of.
I figured the best way to keep the iguana's from being able to dig out was to surround the area with cinder block, and of course than realized this would be an ultimate pond surround. My first plan was to add the pond at some future time; but I realized that would be a LOT of work once I had the cage up. So, I started digging.. Note the sprinkler line running across the 'pond' about 2-3 inches down from the surface (above the lower layer of block, near the middle blocks). Had to make a 90 degree on each end and dig it down further.