You have to be very careful about using a billboard liner. I have actually heard a few horror stories of them. Some come with tiny holes in them, some don't hold up for more than 5 years or so in brutally cold temps, shipping can be astronical, it doesn't "stretch" well when placing it into the pond, etc. I can tell you that just working with a regular pond liner is very hard work, it's extremely heavy. I've heard billboard liner is even heavier. On the other hand some people using billboard liners have had no issues. Whatever you choose, be sure to put an underlayment beneath the liner, as the weight of the water will press it into the ground, plus rocks/stones beneath will shift beneath the pond during winters and time. I shudder to imagine ever having to replace my pond liner, it is hard, time-consuming work, and looking for leaks can be like looking for a needle in a haystack, too.