Patio, Pool + Garden
If you have an undercover alfresco area that could benefit from some timber battens, it may even be possible to use a noise-absorbing material backing, such as gauze or scrim, which will further soak up the sound.
Resin-bound gravel [pictured here] is permeable. You often see it under trees in public areas. It provides a bit of cushioning and can easily be hosed down. You can create interesting curves and get lots of different colours.
Red-hot pokers [Kniphofia, seen here]
Geums [the pale orange flowers seen here]