What you think about an option that prevents deleting a folder (incl. files/subfolders)? I know that can be solved by using NTFS or set write-protection or recycle-bin on most devices, the idea just came after I wanted to delete some folders and accidentally switched destination to active in dual-view and deleted selected folder there (recovery was no prob!).
Hmm, i like that idea & think, that i've suggested something similar quite a time ago. I could imagine something like the @ifpath command,
that could be set to require a password for deleting files, like @ifpath:D:\music* ../ DELETE passwordprotection=12345.
Why not use NTFS permissions instead? You have a solution so adding another way to do the same thing, and the time and complexity that comes with it, only makes sense if there is something wrong with the existing solution.
I don't know how you would list all the folders you might not want to accidentally delete, either, unless you just had a whitelist of folders you did want to delete. If the problem is accidentally clicking delete on the wrong side then that could happen when folders you sometimes delete from (and thus don't have protection on for) are on either side. I'd say it would actually be bad to get used to not having to think before you push delete, because there are always times when you really do have to think. (And the existing delete confirmation option, on by default, handles the general case where you want to confirm deletion for all folders.)
Why not NTFS? Because on some devices FAT32, ExFat, etc. is required (e.g. MicroSD-Cards in phones, multi-bootable devices,...) and on external devices you might get problems when using on different machines.
Leo, I (and most others) surely delete a thousand times before I delete something by mistake - I always thinking! But nobody is perfect, you can oversee things and under working-pressure such things simply can happen. So there was never a DO-version that has been published, where you did overseen something by mistake and corrected it quickly 
? Wow 
!
But hey, making good/useful suggestions for DO is not easy, as it already offers so much options! I can live without this suggestion (as I can recover my files or have a backup), but if there would be some kind of "blacklist" - I would use it!
Hmm, I just don't think many people would go to the trouble of creating a list of all the folders they would never want to delete, such that the feature could save them from doing something by accident (which, from Murphy's Law, will always be on a folder you never thought you'd accidentally delete and never added to the blacklist). Especially if we're talking about external drives with non-NTFS filesystems, where you'd have to plug them in on-by-one to make that list (and hope the drive letters never change, unless you remembered to use label aliases, which most people don't know are there).
Although, as Abr said above, you can already create such a list using @ifpath if you want to give it a try.
I agree that making such lists would be just another thing you have to think about.
You may also:
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Mark files/folders as read only and set DOpus to ask for confirmation when deleting such items.
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Consider using recycle bin.
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Don't delete any files with a single button but instead set hidden attribute and add the item to "delete these items later" collection which you would clear from time to time.
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You can always make a button to run yourApplication.exe {filepath} which would check the path, compare with data base containing white/black lists and run delete command via dopusrt.exe if it the path matches some criteria - if that helps in anything.
the same thing as op happend to me , folder in right pane was deleted instead of the one in the left pane. but it was not recoverable.
just a rightclick -> lock folder should suffice
Such a thing doesn't exist in Windows, other than by changing the folder's permissions (discussed above already).