The old dog for the hard road.

This expression means that experience is invaluable when one is faced with a difficult task.
"The case calls for an experienced lawyer, an old dog for a hard road."

It's used to describe a person who has survived many difficulties and has learned much from the experiences.

There are certain tasks that require seasoned judgement and resilience. It would be a mistake, to entrust such an onerous challenge to a novice. 

Refs e.g. 

https://www.phrases.org.uk/bulletin_board/24/messages/136.html

https://www.learn-english-today.com/idioms/idiom-alphalists/alpha-list_D/id_D6-dog-doghouse.html