How do you keep the shield in place? Presumably Earth's gravity is enough to counteract the push of solar winds, but this is suggested to be a much smaller object (albeit closer to the Sun [edit: assuming Mars' L1 is between the Earth and the Sun]).
[Edit 2: Or are the solar winds constant enough to just shift the L1 to a different equilibrium point?]
It can use the very solar wind to steer itself. And L1/L2 are very close to Mars, Earth is much farther.