How to use magnets when hiding a cache
An excellent free source of small, powerful magnets is to take an old PC hard disk to pieces. There's an excellent article about this here with pictures showing how to take the screws off, etc. You may be able to beg one or two broken drives from a PC store, or from a friendly geek.
The magnet tends to be arc (banana) shaped, typically attached - apparently with some form of glue, although you wonder why that's necessary - to a similarly-shaped but larger piece of steel. You can chip the magnet free with a hammer and chisel - it will probably break, but this isn't a big problem, as you probably don't want to use all of it anyway. You can also break the magnet into smaller pieces the same way, but beware of the very sharp edges which can result - these actually seem to be from the shiny covering rather than the main body of the magnet, and are easily filed down - with a non-steel file :-)
You now have a number of very small (and especially, very thin) and powerful magnets. I like to place them on the sticky side of camouflage duct tape which I then apply to the outside of the cache box.
There are two disadvantages to this approach: (1) keeping two pieces of magnet apart while applying the tape, and (2) sometimes when the finder takes the box, the magnets will stay in place and the tape will tear off!
A workaround for (2) is to find some way to stick the magnets inside the container. However, you lose quite a bit of the magnetic force this way, and it can be quite difficult to get most forms of glue to stick, especially to polyethylene-based plastic containers.
My most successful magnetic microcache is made from a selection of large plumbing nuts and bolts. The magnets - just two small shards from a hard disk magnet, perhaps 4mm square each - are superglued to the outside, and it's hanging from an airconditioner bracket. It's in plain view, but it looks just like it belongs there.
Nick (gc.com: "sTeamTraen")