  In a hard-wall model of holographic QCD, we find that nonlinear boundary
dynamics are required in order to maintain the correct pattern of explicit and
spontaneous chiral symmetry breaking beyond leading order in the pion fields.
With the help of a field redefinition, we relate the requisite nonlinear
boundary conditions to a standard Sturm-Liouville system. Observables
insensitive to the chiral limit receive only small corrections in the improved
description, and classical calculations in the hard-wall model remain
surprisingly accurate.
