I think most bikes get stolen by 2 or 3 big guys lifting them into a truck or van. If you are worried about that, get a heavy chain/cable and lock and lock the bike to something sturdy like a power/light pole or an eye bolt in cement. Put the chain through the bike's frame and/or wheel. A cover will make it less attractive as they won't be sure what bike it is. Leave the bike where it can be seen but not easily knocked over. Alarms seem to be more trouble than they're worth. No one pays much attention to them and they have a habit of draining batteries.