With
B3: (containing the Data Validation cell)
• Set Cell B3 to UNprotected
• Set Cell C3 to PROTECTED
• Select cells B3:C3
• Home.Format.Format_Cells...Alignment_tab
• Check: Merge cells
I generally avoid merged cells, but in this case they are helpful.
Last...Protect the worksheet.
The end result:
Users will be able to select items from the dropdown list
but will not be able to delete the contents or paste
data into the cells.
Note: There are ways around that meager security, but
at least the users won't inadvertently ruin your sheet.