In battle
Rock Head prevents recoil damage from moves (except Struggle, Shadow Rush, and Shadow End).

If a Pokémon with Rock Head uses a contact move on a Pokémon with Mummy, so that it gains Mummy after inflicting damage, it does take recoil damage from that attack.

Rock Head does not affect other kinds of damage, such as crash damage, damage from a Life Orb, or damage from a Jaboca or Rowap Berry.

Outside of battle 
Rock Head has no effect outside of battle.

In battle
Along with its previous effects, Lightning Rod also gives the Pokémon immunity to all Electric-type moves, and raises the Pokémon's Special Attack by one stage whenever it is hit by an Electric-type move. Electric-type multi-strike moves (such as multi-strike moves affected by Electrify or Electric-type moves affected by Parental Bond) will only activate this effect once. If the Pokémon is protected from the move or immune to the move due to being Ground-type, its Special Attack will not increase.

Lightning Rod can now redirect Electric-type Hidden Power, Judgment, and Natural Gift.

If a Pokémon with Lightning Rod is holding a Cell Battery, Lightning Rod absorbs the move, so the Cell Battery's effect is not triggered.

In Triple Battles, Lightning Rod cannot redirect Electric-type moves if the Pokémon is out of range.

Outside of battle
It is unknown if Lightind Rod has an effect outside of battle.