If by "hammock" you mean some fabric suspended between the decking and the fence I think you may be on to a loser.
Stones are heavy. Unless very firmly supported they will try to do what gravity intended - stretch the netting and touch the ground for support.
Depending on the drop from the edge of the decking to the ground, I would be inclined to consider fixing boards to the side of the decking and the fence to form a wood sided "trench". This can be filied with stones or rubble/mud topped with decorative stones.
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