To stop your bike from being stolen you have to think like the thief.
First, they need to know what the bike is, this is where the cover comes in. Now they are forced to walk up to the bike to case it out (lift up the cover). This is where parking the bike at the far end of your spot and the alarm comes in. Basically they will trip the alarm lifting the cover and they have no interest in loitering in the spot if the alarm is going off. Odds are they did not get a really good look, but they know there will be some noise if they look again or come back for the bike. Next is the chain, yes they can cut it without much fuss but it is another step that will slow them down.
Or you can leave the bike in the open so they do not have to be bothered with the above.