Ok that means you have a DSO Server type and not a CGI Server type. The AutoLock button is only displayed for CGI Server types. Ok try these steps below and let me know if your root htaccess file is automatically changed again or not.
1. Deactivate all of your other plugins except for BPS Pro.
2. Click the Create secure.htaccess File AutoMagic button.
3. Select the Activate Root Folder BulletProof Mode Radio button and click the Activate|Deactivate button.