You can just use the click event:
Private Sub Check0_BeforeUpdate(Cancel As Integer)
varReply = InputBox("Requires password to continue", "Enter Password")
If varReply <> "password" Then
Cancel = True
End If
End Sub
Not the most secure. If you want to get fancier you can create a userform with a masked password, and there are routines to hash the password so you don't have it stored in code.