Dynamic Data Protection

Hi all

In order to protect a spread-sheet from accidental alteration of existing data - I felt it would be ideal to protect the new data that has been inputted (like a dynamic protection of data so to speak)?

So if I enter something this week, I will not be able to make changes (whether accidental or not) to previous data i.e including that entered last week.

This way, it is safer and I also have a backup of the excel sheet each time it is closed plus it is automatically saved (without user intervention).

Any ideas on dynamic protection anyone? Thanks

Usman