We present a concise formulation for two-way fluid–rigid coupling in Smoothed Particle Hydrodynamics (SPH) based on a single boundary layer enhanced by a simple volume-corrected mass. Traditional multi- layer sampling ensures complete kernel support near walls but at a significant computational cost. We show that a single layer— augmented by a corrected boundary mass—preserves stability and accuracy in common scenarios, including thin or complex rigid geometries. A compact implementation integrates with standard WCSPH/PCISPH/position- based solvers without custom boundary forces. In a representative setup, the approach reduces fluid–boundary interaction counts by more than twenty percent while maintaining robust two-way coupling. We also outline how the method translates directly to critical infrastructure analysis (dams, levees, gates, and dense urban blocks), enabling faster what-if studies for flood mitigation