I have to echo some of the comments from TFA. If you mark it, no matter how, the curious are going to explore it. Even if they understand the danger they may unearth.
The exception is if you have an advanced culture that stumbles upon it. They'll know what it is and perhaps how to deal with it better than we do.
I have to admit that I find it hard to imagine an alien mind not having curiosity or the urge to explore.