Welcome aboard bdog

Dave is right deeper is better, you will loose a lot of water to evaporation around Lubbock. Even with a well it will be hard to keep the pond full. Not sure how much homework you have done but A liner will need to be covered for it to last very long.
bentonite is a good product but it must be installed properly od it will not work. There will be some liner companies around Lubbock and the will make what ever you need, There will also be some bentonite companies close by check prices.