Boundary walls and pools both need council approval in most cases, and both have their own technical rules.
Walls
Freestanding walls over 1.8 m and retaining walls need plans, and your zoning scheme may restrict street-facing walls. Retaining walls hold back soil and fail badly when they are built like garden walls; above a modest height they need an engineer's design.
Pools
In Johannesburg and Ekurhuleni a swimming pool goes through as a plan submission, and the drawings must show the pool's position relative to the boundaries and the house, and how the pool is made safe for children. SANS 10400 sets the safety rules for pools at houses.