Triangles are good. They keep rectangles from parallelograming. I would recommend diagonals either forward or backward in the rear side areas like this: That will greatly improve the cage strength. Then do away with the proposed low horizontal bar, It's really not doing anything to strengthen the cage. Also, your additional horizontal link at the top is redundant with the one that's already there, but it's definitely nice from an aesthetics standpoint. The diagonals up top are a good idea.