To protect your pond liner from UV damage, your main strategy should be minimizing exposure to sunlight. Start by covering the edges of your pond liner completely with rocks, gravel, or soil. Since very little UV light can penetrate deeper than 12" of water, introduce floating plants or water lilies and marginal plants in the shallow parts of your pond by providing shade while enhancing the pond's aesthetic appeal.
If planting is not feasible, you might consider installing sails, shade cloth, or netting over the pond, which can effectively filter sunlight while still allowing for air circulation and rainwater entry. Happily, all these methods have an added benefit of reducing algae growth. Whatever method you use, be sure to inspect the liner for signs of UV degradation. Significant degradation may require replacing the liner altogether.
