The red ball thing is a piece from an old lawnmower. For the opening, I cut a hole in the deer fence material and wrapped the edges with garden twine. If you can’t fit a square peg in a round hole, how about a round peg in a square hole?!
In the process of redesigning/moving the gate we also moved five of the fence posts out about ten feet, so now the “corner office” and grassy area on the east side of the garden is way bigger:
More about the Spy Garden deer fence: