Record level security in salesforce

How to provide security for the records?

we actually have four ways of setting record-level access rules:
1. Organization-wide defaults
    * OWD allow us to specify the baseline level of access that a user has in our organization.
    * OWD provides default accessibility for the owners and other users of the organization.
    * Either we can set public or private.
    * For public again we can set like below:
       - public READ/WRITE
       - public READ ONLY
       - public READ/WRITE/TRANSFER (only for standard objects)
       -many more options for the standard objects
2. Role hierarchies
    * It allow us to make sure that a manager will always have access to the same records as his or her subordinates.
3. Sharing rules
     * It allow us to make automatic exceptions to OWD for particular groups of users.
4. Manual sharing
     *IT allows record owners to give read and edit permissions to folks who might not have access to the record any other way.