How do i make a div that will not break even if the structure of the information inside it is improperly made.

ie:

```
<div id="bulletproof_div">
    <div> </div>
    <div> </div>
    <div id="unclosed_div">
</div>

<div id="normally_this_one_would_break">
</div>

```

edit: the context is that it is a mailing system where i have no control over the information that is being sent to me, that is why i need to make it so that the website will not break.

i have tried successfully with iframe but i need to be able to modify the inner html of the div so iframe is not ideal. 

Thank you for reading