The way I understand it, we expect that our waste will outlast our civilisation and that having it lying around in the open will endanger the civilisation(s) that (we fervently hope) will follow.

See wikipedia pages and references for work on this:

Long-time nuclear waste warning messages:

https://en.wikipedia.org/wiki/Long-time_nuclear_waste_warnin...

Waste Isolation Pilot Plant - Warning messages for future humans:

https://en.wikipedia.org/wiki/Waste_Isolation_Pilot_Plant#Wa...

Also, examples of proposed hostile architecture here:

https://wipp.energy.gov/pdfs/site_markers.pdf

And the full permanent markers implementation plan, here:

https://wipp.energy.gov/library/PermanentMarkersImplementati...