What recommendation should be given to a contractor working in a sandbox with sensitive data?

Implementing Salesforce Data Mask is the most appropriate recommendation for a contractor working in a sandbox with sensitive data. Salesforce Data Mask helps protect sensitive information by obfuscating data in non-production environments, such as sandboxes. This means that while contractors can still perform their tasks and tests within the sandbox, they will not be exposed to real sensitive data.

Data Mask ensures compliance with privacy and security regulations, as it allows organizations to use realistic data scenarios without risking the exposure of actual user information. By anonymizing personal data, businesses can leverage the advantages of testing and development without compromising security.

Using session-based permissions is useful for controlling user access during specific sessions, but it doesn't directly address the issue of managing sensitive data exposure within a sandbox environment.

Limiting access to certain objects can help control what contractors see but may not provide the comprehensive data protection that Data Mask offers.

Keeping all data in a separate environment could be considered a basic security measure but does not take advantage of the testing capabilities that can still be utilized with data masking. Therefore, for a balanced approach to sensitive data management in a sandbox, implementing Salesforce Data Mask is the most effective solution.