High stretch (elongation) is often marketed as a benefit, but in a pond, it can cause significant problems. When a 45 mil unreinforced rubber liner stretches over a rock, can thin to as little as 15-mils at stress points, leaving it extremely vulnerable to punctures and tears.
Reinforced liners (like RPE) have an internal reinforcing grid that refuses to stretch, so the liner maintains its full thickness and full strength even as it bridges over small rocks and voids.
