You can lock a project to prevent it from being automatically deleted.
You can lock a job by selecting it in any of the Jobs tabs, and then clicking the Lock button. To unlock a job, visit the Locked tab in the Jobs module, and select a locked build; then click the Unlock button.
The system will not purge a locked job automatically (as when the class purge properties for the run call for its deletion). A locked job can still be deleted manually.
Use the Locked tab to view jobs which are in the locked state. Such projects do not appear in the Completed tab.