I understand your concern, but it's essential to approach this with caution, as actively trying to block user actions like accessing developer tools or pressing F12 can be considered user-hostile. Instead, focus on improving the security of your application and obfuscating sensitive code.
Here's a revised version of your HTML with an attempt to minimize the risk of direct button blocking and F12 detection:
```html
Marcia
```
This version includes an attempt to prevent the F12 key press and right-click context menu, but please note that determined users can still find ways to access developer tools. It's always recommended to focus on securing your application's backend and sensitive information.