The people studying this have generally advocated a layered defense. First, people dig up the strange stuff on the surface if they have a use for it (although it should be designed to make this difficult, expensive and not especially useful). They don't have to be especially advanced to do this, maybe. Second, perhaps they develop the ability to dig deeper and they discover more elaborate warnings. Eventually, they get to the equivalent of a vault where they've received plenty of warnings and, one hopes, are savvy enough to interpret them and make an educated choice as to whether they should proceed. (there's an assumption that wisdom, caution and linguistic ability might grow in a future society alongside the ability to prospect and dig, which might or might not work out)

The strange spikes and so on are just one possible approach. Simply hiding the stuff a mile under some salt can work and at least one site does that. I think you're going to see a ton of stuff hidden that way just because it's the path of least resistance once the regulatory permissions are secured (which is hard enough). I think this approach has been written about in the NY Times and so on.