My first fence post was so shallow, a stiff breeze had it leaning like the Tower of Pisa. @fisher.michael isn't wrong about society cutting corners, but I took it to an art form by barely covering the base with soil. After a mild rain, the whole section swayed like it was dancing, and I had to redo everything with proper depth. Now I always dig at least a foot deep, even for short dividers, because skimping just costs more time later.