i built a pond for mom mom a couokle years ago but didnt have the money to fix it up nice so i just ended up trhrowing it together and i know want to make it in to a concrete pond insteaD OF THE PLASTIC LINER I WAS USING BEFORE can anyone help me with this please? its about 7 feet long and going from 4feet to 7 feet wide at the widest point. Its about 2.5 to 3 feet deep rectangular shape with walls strait up please help me?