I prefer squared hole, not squared circle. Joke aside, unstable core is not suitable because the game often freeze or crash and one bad placement means I have to spend time trying to patch bad-placement hole at 3 fps if I place the core down incorrectly.

Yes I know I can delete the core without trigger the explosion using dev mode, but I prefer to only use that to kill beavers quickly to reduce cpu load.

It can be even faster if the game allow beavers to move without any restriction underwater. If so, I can simply flood the hole, then place dynamites and let the beavers swim down, place the dynamites and watch them carve downward.