Permission based content blocks

I’m having a problem with some of my users accidentally fouling up page and post content layout, by editing areas of code while they’re meant to be just editing content. Is there a way of me creating the ‘core’ page content and leaving dummy text within the content blocks for users to replace with their own content, which at the same time prevents them from being able to edit ‘preserved’ items, like div tags, shortcodes, etc? I don’t mind if they can see the ‘uneditable’ tags, although to avoid confusion it’d probably be best if they couldn’t, just as long as they were unable to change or delete it! Maybe a plugin that allowed code to work within the editing window and I could then set a class for shortcodes to hide them, but then thinking that through, that wouldn’t work as they’d also be hidden when the page came to be rendered.
It seems like an obvious problem that someone would have had before and worked a way round, but I’m not finding it!
Apologies if in the wrong area _ wasn’t sure where this belonged