I love the Master combination padlock. http://www.masterlock.com/apps/maste...tial/homeyard/

You can get it at home depot or Lowes.

I have a U-lock on the bike rack at work, which I leave there. I also have a long 9 foot cable combined with the combo padlock. When I go on evening rides with my wife and kid in the trailer I can cable through all three conveyances and lock them up together to an immovable object. Not necessarily high security, but way more expedient than trying to individually lock two bikes and a trailer.