You also need to consider the type of plastic. Most types of plastics are not made for use with fish and can bleed toxic chemicals into the water over time as is the case with Polyethylene.
The heavier plastics are more expensive but as with (Firestone EDPM) come with a 20 year warranty against UV degradation. I have used this several times and it lasts long and doesn't puncture easily. Covering it with soil though would mean slower tapered shorelines or the soil would tend to erode and slip down the plastic.
Barry
