I use the public sandboxes (whichever one is least crowded), and on a few occasions have had problems with griefers. Shown in the image is the solution - a personal sky platform on which to work. The idea was unashamedly taken from something I'd seen on SL Boutique, although there's was far more impressive in appearance and features.
At the moment it simply rises to a high altitude and centers on rounded coordinates, but I might add more features if they seem necessary. For example, why build in a feature to descend when its more fun to delete it and land by parachute?