
{
Prevent users from pasting text in your Memo.
}

uses Clipbrd;
...

procedure TForm1.Memo1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if ((Key=Ord('V'))and(ssCtrl in Shift)) then
  begin
    Clipboard.Clear;
    Memo1.SelText:='Delphi tricks rules!';
    Key:=0;
  end;
end;
