Many shallow water acoustics techniques require accurate estimates of the propagating modes from pressure observations at a vertical array. The noise in these estimates is a function of the conditioning of the vertical modes as sampled by the hydrophone array. However, the sound-speed profile and thus vertical mode shapes are usually not known when the array is designed. In addition, economic considerations often dictate the same array be used in a wide range of environments. Consequently, optimizing the array for a specific environment risks a degradation in performance if the experimental environment differs from the environment assumed by the array design. Conventional wisdom holds that in the absence of precise environmental knowledge, the safest approach is to space the hydrophones evenly throughout the water column. This work presents several simplified mode filtering scenarios demonstrating that nonuniform hydrophone spacings exist which are more robust in the minimax sense than uniform spacing, if it is possible to specify a range of operating environments for the array. This means that their worst case performance is better than the worst case performance of the uniformly spaced array over the range of environments.