Similar to steel wool, copper wool is another option that can act as a barrier for mice. It is also resistant to corrosion. Using a high-quality caulk or sealant designed for exterior use can help create a tight seal around the openings. Silicone or polyurethane caulks are good choices for their durability. Also, you can install metal flashing or mesh around the pipe openings. Secure it tightly to the floor to create a physical barrier. Make sure there are no gaps for mice to squeeze through.