Oh, I imagine unplanned and reentry would likely make it very hard to locate, if not destroy the contents in the process. Decaying orbits would mean it's likely to happen, too. But I think if a civilization has the capability to reach an orbit, it's likely they have the technology to find something in orbit, or will shortly.
A better plan might be to create a structure on the moon to house it, and create giant triangles in the landscape of the moon visible through telescope that point towards it. The moon is fairly stable to my knowledge (except for meteorites, but I think that can be somewhat mitigated depending on the time frame we are talking about), and people always like looking at the moon through telescopes...
And we should make it black and rectangular shape. I suggest we call it the monolith. We might want to put a few of them around the solar system just to be safe.
A better plan might be to create a structure on the moon to house it, and create giant triangles in the landscape of the moon visible through telescope that point towards it. The moon is fairly stable to my knowledge (except for meteorites, but I think that can be somewhat mitigated depending on the time frame we are talking about), and people always like looking at the moon through telescopes...