Much easier to stay with just the rectangle. Use small bundles of 1 foot long pvc for spawning that are easy to add and remove from the pond. Put them in for spawning and take them out to seine. Once you seine add them back and put back enough FH to repopulate. You can also use the seine to divide the pond into 2 parts and simultaneously grow 2 species ( do a search for blocking nets here). Good articles in PB mag on forage ponds and blocking nets.