Have you ever considered that overwatering landscape can not only waste water but cost you in the long run? It is a very common finding to discover water damage to retaining walls (and even the foundation of the home) from excessive water that works its way into the composition of the wall. Over time this will destroy the structural integrity of the wall and ultimately will cost the home owner considerable costs to replace.
Long term water damage to retaining wall in front yard.
This photo shows the cracks in the mortar as well as the damage to the face from constant water exposure.
Earth loaded retaining walls are especially venerable to damage when exposed to chronic moisture.