I like decorative segmented block wall. It required a gravel base, simple drainage pipe system
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with gravel behind it. It NEVER rots, comes in different colors and finishes. You can run curves in it, change the heights from one end to the other and if ever damaged, only have to replace the damaged section. I build these walls on a regular basis walls. It's affordable and a beautiful finished product that lasts a lifetime. If you have more questions, please let me know.