[Empireoftheatom48]

Unless you give the planet a magnetic field like earth your out of luck. The solar wind will blow it all away. Like what has already happened.

[DannyTN]

Apparently you need to do both increase mass and create a magnetic field. Mars already has a slight magnetic field, but it's not strong enough to protect it.

Sending a comet or asteroid into orbit, thus making a moon could help with the magnetic field.

can we create a magnetic field for Mars