lifeguard

A lifesaver: a rescuer, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water.

A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.

"The people's love is the king's lifeguard."

[I]n the reserve were the king's lifeguard, commanded by the earl of Lindsey, and prince Rupert's regiment of foot[.]

A sturdy metal bracket fixed in front of each of the leading wheels of a train to deflect small objects away from the wheels to prevent derailment.

It also looked at what effect stronger lifeguards might have had. They protect the leading wheels from small obstacles and in modern trains have coped with hitting landslip debris.