A novel tri-layer approach for immobilizing metal nanoparticles in SiO₂ supports is presented. In this work, we show that under rapid heating to temperatures of approximately 1, 000 ℃, metal nanoparticles less than 15 nm in size will entrench in the SiO₂ layer on a silicon wafer to create pores as deep as 250 nm. We studied and characterized this entrenching behavior and subsequent nanopore formation for a wide variety of metal nanoparticles, including Au, Ag, Pt, Pd, and Cu. We also demonstrate that an Al₂O₃ layer acts as a barrier to such pore formation. Thus, by creating a tri-layer architecture consisting of SiO₂ on Al₂O₃ on silicon wafers, we can control the depth to which nanoparticles entrench between 3-5 nm. This small range allows one to entrench particles for the purpose of immobilization but still present them above the surface. The two advances of moving into the sub-15 nm size regime and of controlled particle immobilization through entrenchment have important implications in studying site-isolated and stabilized metal nanoparticles for applications in sensing, separations, and catalysis.