I would've never thought to use river rock at the base of potted plants/at the edges of the patio, but maybe that could work. A larger, flat top rock could even act as a riser for a led candle lantern, etc.
Transform your balcony into a mini garden. You can do this with help from an array of potted plants, wooden chairs and bamboo walls. Pick out various tropical plants, flowers and cacti to complete the look.