Several posts recently ask how to work around outlet or ceiling fixtures with drywall. You can measure carefully and hope it all matches up. My fave drywall guys turned be on to this concept. They come in sizes to fit all boxes from outlets to ceiling mounts. You bury them in the wall and then sense them. Then you use your rotozip or other rotary drywall saw and I promise, nice neat holes every time. Yank the suckers out of the wall or ceiling if you get the ones for fixtures. Use them over and over again. They are hardly high tech but really clever I think. Nothing more than magnetic attractive material with a strong plastic shell your roto tool can wack.