I bought 100 neodymium boron super magnets. They are just a little smaller than a penny, but a little thicker. I just start waving them over a wall, and in no time, I have 10-20 of them sticking on the wall, and they REALLY tell me where the stud is. They also work good defining nail guards that send stud finders into convulsions. From there, I can take the old Zircon and fine tune.
STeve