Prevent/Stop Workbook Closing Via Top X

i am using the following code to close my userform and work book,this disables the exit button on the userform but i can still close the workbook by using the exit buttons on the sheet. can i disable the exit buttons on the sheet so the only way to close the workbook from the userform

Private Sub CmbClose_Click()

Dim ans As Variant
ans = MsgBox("This will close XL, save current file?", vbYesNoCancel)
If ans = vbYes Then 'save book and quit XL
ThisWorkbook.Save
Application.Quit
ElseIf ans = vbNo Then ' no save and quit XL
Application.Quit
ElseIf ans = vbCancel Then 'no save, no close , back to userform1
Exit Sub
End If

End Sub