In short, there's really nothing you can do to secure your tent. Best you can do is try to ensure it's as unattractive a target= as possible. Pitch it in a highly visible spot, where there are apt to be people around fairly often (OK, I admit, during the concert itself this probably won't do any good). Maybe leave a small transistor radio playing softly inside, so someone walking by thinks someone is in the tent. Leave as few valuables around as you possibly can. And, if you're camped near a tree or some other formidably rooted object, zip your gear into a duffel bag and attach that to the tree or telephone pole with a PacSafe 140 ($75, www.pac-safe.com), a duffel-sized stainless-steel net that wraps around your luggage then can be locked to some immovable object. It won't fully deter a thief with cable cutters, but it will slow them down while discouraging the snatch-and-run variety of thief.
The same rules really can apply to anybody camping out, whether in a campground or even on the trail. Mainly, try to remove temptation from easy sight.