Once I started digging further, I ran into some PVC conduit. I REALLY didn't want to dig those down, and re-wire, so figured that was how far it was going down on that side. I put the sprinkler line just under that level, so in the beginning, I had a 'deep side' on the right, separated by the sprinkler line. Later, I decided I may as well make the 'deep' side (about 3.5 feet) even all the way down, so dug the sprinkler line even further.
The block is 2 levels deep, and I cemented them in entirely. It may have been overkill, but I figured this way, it wasn't going anywhere. I also put 2x4 just on top of the block, on the 3 sides, so there was no place any of the inhabitants could 'push' their way out of screening or any other sort of barrier. This also provided a mounting board for the bottom of the metal screening.
On the upper level in the back (closer to the front in the picture), I left a space between 2 of the blocks. This was for a 'proposed' skimmer type filtering system for the pond, which, if it didn't work out, I could simply block in the opening.
The back wall, the existing block wall, was obviously 'dig proof'. Just to the left of the pond in the back, starting the other side of the L, was a cement pad - which originally was there for the propane tank that used to heat our pool. This pad goes from the wall to the other side of the cage. Next to the pad, to the 'top' of the L, I also buried more cinder blocks, and over here used a 2x6 on top of that (the blocks and pad). The very top of the L has a hinged door, about 3 feet wide x 6 feet tall, for easy access to the cage area. This also has a buried layer of cinder block under it. Again, no digging here!