If you want to hide sheets and then stop people unhiding them, here is yet another technique.
Hide the sheets as per normal, right click a sheet and choose Hide.
To hide more than one sheet at a time you can use the Ctrl and Shift keys to select multiple sheets and right click the selected group and choose Hide.
Click the Review ribbon tab and click the Protect Workbook icon.
Make sure the Structure option is ticked and enter a password (you will have to enter it twice).
Click OK. Make sure you make a note of the password – you will need it to unhide the sheets, delete sheets or add more sheets.
This password doesn’t impact entering values in a sheet.
Excel passwords are not very secure and can be easily removed so this is not a secure solution.