Something I've never quite understood... (Why a Ring?)

This may or may not be a ridiculous question. But I've wondered this ever since I first read the books, eight years ago, and I'm wondering it still. Perhaps one or more of you will have some insight into this.

Why on Middle-Earth did Sauron pour his life-force into something as small and, more importantly, easily misplaced as a ring?

Granted he wouldn't expect it to ever leave his hand, but surely someone as intelligent and skilled as the Dark Lord should have had the foresight to build in a fail-safe. At the very least, it could have been something a trifle larger- say, an armband? The Lord of the Armband wouldn't have sounded as cool as the Lord of the Ring, yeah, but it would be easier to track down, yes?

Furthermore, why tie your life-force to something physical at all? Why not ferret it away on the astral plane or somewhere else safe?

Also... what would have happened had one of the rings of the Nine been seperated somehow from its owner? The Nine are halfway between living and true death... so, if such a thing were to happen, could it swing either way? The reason for this second question is a resultof a roleplay begun by myself and a group of friends, who set up a sort of 'what if' scenario: What if the aforesaid situation were to happen? What if someone were to be stabbed by a Morgul blade and didn't find healing in time?

The result was actually great fun- we had a female Ringwraith (the result of the latter situation) wandering about, and played around with both of the speculated outcomes in the former scenario. But still, the questions remain.

No disrespect is meant for the aforementioned beings/people. My friends and I are all officially part of the "We Love Sauron" cult, which seems to be distressingly small these days.