A Nokia 3310
A grain of sand, dump it in the ocean
I was thinking the same thing, except a rock. I frequently visit ships as part of my job, and it would be no problem dumping it somewhere it would be likely to remain undisturbed for the rest of eternity. A grain if sand is likely to move with the currents. A rock will not.
But then your loyal servants won’t be able to find it either to bring you back.
A screw thats about to be fired into space and ejected off into the infinite great beyond.
Can’t do shit about my horcrux if it’s floating out past nebula 12.
There’s a fan fiction where Voldemort (probably) horcruxified the Pioneer 11 plaque.
That kind of thing was going to be my answer to this question also.
The main downside I can think of, is a Horcrux similar to a Lich Phylactery in that you have to reform adjacent to it?
Nice try, Al-bum.