Invent better stuff.
About 25 years ago, a huge "umbrella" of metalicized mylar ribbon was proposed to be sent into outer orbit: its orbit would place it constantly between the Earth and the Sun—spinning slowly to retain its shape.
Depending on how much of the Sun's rays needed reflecting (to cool the Earth), the number of ribbons included could be determined before construction. This probably appeared in Popular Science magazines that I subscribed to. The authors didn't mention how it could be "retracted" when no longer needed, but something on the order of "chain-shot" could have done the job.