Local scour around bridge piers remains one of the primary causes of bridge failures worldwide. Conventional countermeasures such as riprap and collars often suffer from stability issues and edge failure under high-velocity flows. This study introduces a novel countermeasure using Interlocking 3D Porous Blocks (IPBs) to protect the sediment bed around square bridge piers. Experimental investigations were conducted in a laboratory flume under clear-water conditions. The effects of the number of block rows (initially 1–4) and vertical placement level (on-bed, semi-buried, and fully buried) were systematically examined. Based on the superior performance of the buried configuration, two additional five-row arrangements (a single buried layer and a double-stacked buried layer) were tested to identify the optimal design. Results demonstrated that the buried configurations significantly outperformed others. The optimal configuration, consisting of the double-stacked, 5-row buried layer, resulted in no measurable scour within the accuracy of the adopted measurement system (±1 mm). This design effectively dissipates the energy of the downflow and horseshoe vortex while maintaining bed integrity. The mechanical interlocking system provided excellent structural integrity, making IPBs a highly promising solution for bridge foundation protection. Field-scale validation is recommended for practical implementation.