This is a much more reasonable idea once you're on Mars, and current research offers some hope that it would actually work. More worrying though is the trip to

This is a much more reasonable idea once you're on Mars, and current research offers some hope that it would actually work. More worrying though is the trip to Mars, which would have a much higher exposure and require some really novel shielding. The best way for that to happen, short of a breakthrough in materials science, is to build the shield outside of our well, with materials we didn't have to lift. This is in large part why I think that Mars is continent upon offworld mining and construction industry, rather than the other way around.