Backstop (noun)

1. A barrier or obstacle that prevents something from moving forward or escaping.
2. A safety device or measure that prevents a problem from occurring or recurring.

Origin:

From the verb backstop, meaning "to act as a barrier to prevent something from advancing or escapin.g"

Examples:

1. The wall was built as a backstop to prevent the river from flooding the town.
2. The backstop put in place by the company prevented the machines from malfunctioning.
3. The pitcher's backstop was his catcher.
4. The backstop on the rifle prevents the bullet from traveling too far.
5. The backstop in the contract protected the company from financial losses.