I use 2 locks, a predator chain and padlock and an Abus granit D lock to secure bikes together and to rack...... I then use 2 krytonite cables looped through both bikes and attached to towbar coupling with a padlock under rear bumper. I was going to use a chain but length would have to be so long it would be to heavy.....
I have to audible alarms as well for when parked up