Backing up "Shared"

Help… I have an Excel workbook that is “shared� and updated by multiple
users. I am having issues with users deleting information and saving the
workbook which is overriding the original. Can anyone give me any ideas on a
good backup system? I only have so much room on my company’s server to back
things up so backing it up after each change with multiple users saving
several times a day is not an option. Is backing this workbook up the way to
go or is there a better way to fix my issue? Any help would be greatly
appreciated. Thanks in advance….