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Moss between stone
Dig out the patio area about 6 inches deep, fill it with gravel, then top it with a thin layer of coarse sand. Set each piece of flagstone into place like puzzle pieces, leaving roughly the same amount of space between stones. Gaps can be filled with sand, gravel or ground cover plants.
Retaining wall and lighting
No lip to step over
When the outdoor space is at ground level, and the architectural design doesn't allow for a full-length overhang, a narrow transition strip between inside and out will likely do the trick. A gravel bed with a drainage channel below can be an effective way to keep water from building up and running into the house.
Like the half wall in the pool next to the fence- nice transition to property boundary