Computer simulation is used to examine the spatial distribution of frustrated plaquettes in a square lattice of random +1 and -1 bonds. While the bonds are uncorrelated, the frustrated plaquettes are not. The average separation of a frustrated plaquette from its nearest frustrated neighbour shows a feature consistent with Schuster's pair dissociation transition at c=0.707, where c is the concentration of positive bonds. It also possesses a narrow peak at c approximately=0.9, which may be related to a phase boundary in the Ising spin system on this lattice.