Once the file is opened, you can protect the sheet with code like the following:
Sub ProtectSheetClients()

  Dim wb As Workbook
  
  'Set the workbook to the Workbook containing the file you want to protect
  Set wb = ActiveWorkbook

  'Use code like one of the following to protect the sheet
  'Use the Macro Recorder if you need different options
  wb.Sheets("Clients").Protect
  wb.Sheets("Clients").Protect Password:="foo"
  wb.Sheets("Clients").Protect DrawingObjects:=False, Contents:=True, Scenarios:=False
  wb.Sheets("Clients").Protect DrawingObjects:=True, Contents:=True, Scenarios:=True, AllowFormattingCells:=True

End Sub
Lewis