An idea came to mind today. I was thinking about trees with thorns. Then I began wondering if any trees or shrubs produce thorns or spikes on roots that could puncture pond liner. Being an arborist that's planted trees for years, you would think I'd have the answer. But I'm not all that brilliant. Anyhow, my first question is, is anybody aware of plants or trees that may have sharp parts on the roots system? Then, are there any out of the ordinary puncture hazards that are still common enough to keep in mind? Chips from quartzite flagstone is one little monster I've encountered. When I line ponds with quartzite, I don't fine-tune the edges with a rock hammer by the pond anymore. I take the stone away from the pond a ways.