Bobby, great approach! Suggestion is, if you want to protect the plants, rather than capping the upper area, just protect the plants from the bottom, and raise above the surface by 12 inches (just in case of flooding or introduction of high water during rains. It also allow the plants to grow toward the surface without restriction.
Decrease your mesh size from a large 1" to 2" square gap down to 1/8" to 1/2". Small fish will actively come in to feed. One they're too big go come and and out, they'll grow inside that isolated area, and again, destroy your plant's potting area.
You already cover the deep implanting of the edging to prevent the fish from sneaking through from below. make sure at least 4" of the netting at the bottom go past the loose soil. When fishes get desperate, they do crazy things. Carps and koi will jump to get to the food sources when something is obstructing their way. Best to create the top as a pyramid shape rather than a flat top. This way, it allow the fish to roll off rather than trapped at the top.
