Not sure of your soil type, but for me it is a no brainer. Because of my soil type I have to go with a liner. The nice thing about a liner is no leak worries if installed properly. To me this would be worth the ~ 15 -20 k + cost for a 3/4 acre liner/installation. I would for sure listen to otto and remove all the muck first along with all of his other expert suggestions. If you have to truck in clay and then line the pond with it you would be surprised how close the expense would be compared to a liner, and even if you line it with clay it's not 100% guarantee like a liner. Just my $.02
