Pool retainer and planter walls are subject to failure more frequently than other stucco walls due to the extreme amount of moisture associated with them.
Once a stucco surface has cracked and popped loose the only quality repair is to remove all the loose stucco and recoat the entire surface after applying the proper mechanical and chemical bonding system.
Planter box walls can be water proofed on the inside to prevent water from seeping through and affecting the stucco.
Where rusty corners are evident they should be replaced with plastic components or eliminated entirely. Treating or coating rusted ferrous metal is at best a temporary repair serving only to preserve the problem for later.
Pool and plant areas will require a regular maintenance procedure with both patching and painting on a scheduled basis to retain an attractive appearance.