How do you secure your bikes while camping?

I had never worried about the bikes walking off when we had WalMart specials. But after I upgraded to Trek, I carried a cable lock with us on the first camping trip. Unloaded the bikes and leaned them against the picnic table while setting up in the dark. Walked out of the camper to see a teenager headed straight for the bikes, he spun around and froze in the shadows, then headed back away the way he came. Bikes were immediately locked to the frame of the trailer and remain that way anytime we aren't riding them now. This was in a very large campground and where our site was he had no reason to be headed to other than to take the bikes.