custo-, custod- +

1. Providing protective supervision.
2. Watching over or safeguarding.

1. Someone having charge, or who takes care, of buildings, grounds, or animals.
2. A person who has custody; a keeper; a guardian.
2. Anyone entrusted with guarding or maintaining a property; for example, a janitor.

1. A situation in which someone is entrusted with guarding and keeping property or records.
2. A position in which there is a responsibility for the custody or guardianship of prisoners or inmates.

A custodian.

1. The legal right and responsibility for raising a child and personally supervising the child's upbringing; especially, a person's right to keep the child in his or her home.
2. Detention by the police or other authorities; arrested and in custody: "The police have taken the man into custody."
3. The state of being held in another person's care or protection.

1. Not involving imprisonment or detention in custody: "She received a noncustodial sentence from the court."
2. In the United States, not having custody of child or not being granted legal custody of a child: "He was a noncustodial birth parent."
3. Not having custody of one's children after a divorce or separation.

Who will guard the guards themselves?

Juvenal wrote this proverb in his Satires and it is applicable to modern times; such as, a reference to situations in which there is little confidence in the people appointed to positions of trust; for example, those who are duty-bound to watch over public funds.

Juvenal may also have been referring to the problem of hiring guards to prevent infidelity among women whose husbands were out of town. Another interpretation could be the advice to avoid assigning a fox to guard the henhouse.

A thousand years in thy sight are but as yesterday when it is past, and as a watch in the night.

From the Old Testament, Psalms 90:4.