Protect a field in table after data entry

I have a client who is working with access.
They use Tables to set up budget information for 3 years.  Once a year is approved, they want to protect 6 fields related to 2008 so that they cannot be changed but all other fileds can be.  There is a field  for each year that is entered as "committed" when that year is final. The updates would only be needed for subsequent years.  Is there a way to do that in a table without having to break up tables by each year? I am not that familar with access so need your help.Start Free Trial