my outside enclosure is 50% standard 6 foot residential fence on one side, 2 high cinder block wall the other. It works very well. BC are cheap, easy to get (home depot, lowe's etc...), and easy to move around if you want to configure things differently. I then placed 2 layers of loose brick I had on top to cover CB holes and the brick is slightly longer then the CB, so it have it stick out 1/4 inch or so into the tank area to provide a small overhang. Not that I think a turlte could scale a completely flat vertical wall, but just in case. Incidentally, when you have opaque walls, they don't try and climb (maybe if their enclosure is too small or not enough "furniture" they will....). When you have see-through walls like wire hardware cloth or chicken wire, they will constantly try and climb out and they can climb! So my experience with CB is all positive... hope that helps.