I have run across a website for used billboard tarps as pond liners. http://www.billboardtarps.com/ . These guys buy used tarps with advertisement on one side and heat weld them together to make basically any size you want. The tarps are two ply with reinforcement inside to make a 20 mil tarp that will supposedly last 10 years or longer if covered with dirt. They advertise these tarps as 100% waterproof. They will run about 16 cents per square foot which is much cheaper than any other liner I have found.
Does anyone here have experience, suggestions or comments about these 'billboard tarps'?