In this study, reversible circuits are revisited to achieve extreme soft-defect awareness in classical CMOS circuits. Defect models in the literature are reviewed and defect scattering is analyzed. A reversible 8-bit full adder is designed in 12-bit block code domain. As a proof of concept, a pair of reversible ALUs are embedded into a microprocessor with block-code encoded data-path. The design is simulated in ams 0.35um process and a layout is obtained for tapeout.