Never leave the bikes unattended, did the stupid thing in Fort William a few years back, left the bikes on the roof of the car d-locked, cabled etc…came back to see the car parked 3 up from mine, bike racks ripped off the car bikes gone, luckily mine still there but made me thing twice.
Now whenever we travel someone stays with the car, quick service stop one goes for coffees or food while other stays with the car and keeps an eye on the bike. Its surprised me the amount of people that stop and look at them then move on when they realise me or my OH are sat in the car watching.