You need to set the EnableSelection property. You are probably protecting the
sheet, but still allowing the users to select both locked & unlocked cells. Tru
something like this:

Sub AAAA()
Call ProtectSht("Sheet1")
End Sub

Sub BBBB()
Call UnprotectSht("Sheet1")
End Sub

Private Sub ProtectSht(ShtName As String)
Sheets(ShtName$).Protect
Sheets(ShtName$).EnableSelection = xlNoSelection
End Sub

Private Sub UnprotectSht(ShtName As String)
Sheets(ShtName$).Unprotect
Sheets(ShtName$).EnableSelection = xlNoRestriction
End Sub

For greater security, you could add a password.