induration. 1. the process of hardening or being hardened.
1 They're weak against the Ice and Water types in reference of erosion, which cause this elements to the ground. 2  They're immune against the Electric type because in real life, the ground is a natural sink of electrons.  The Bug type resists them because many bugs like worms live inside the ground and many of them eat it.
Use ground guide(s). It is always best to use a ground guide or guides to help back because the driver cannot see behind the vehicle and other blind spots in the mirrors. A ground guide is essential in blind side backing, but the driver is still responsible. Ground guide safety procedures are in the appendix.