Requiring a password to collapse a group

Hello - can anyone assist.

I have set up a worksheet which has 3 grouped areas in.  The first two I want the user to be able to collapse and enter data.  The last group I only want collapsed if the correct password is entered.  Does anyone know how to do this?  I don't want to password protect the whole sheet as I still want users to be able to collapse and edit the first two groups.

I have written a macro to if the user pushes the button then a password is required and if the correct password is given, the last group is collapsed.  However I now need to disable the "manual" ability of the user to just go click on the collapse + of the group.  I have tried hiding the row the + sign appears in but you can unhide rows without requiring a password.  

So essentially I only want the user to be able to collapse the last group if they enter a password