The two measures that should be implemented to protect an Amazon S3 bucket against accidental deletion are: 1) Enable versioning on the S3 bucket, which allows you to preserve, retrieve, and restore every version of every object stored in the bucket. This helps in recovering deleted objects. 2) Enable MFA Delete on the S3 bucket, which adds an extra layer of security by requiring a multi-factor authentication (MFA) device to confirm the deletion of objects or versioned objects. These combined steps provide a robust solution to protect critical data from unintended deletions.