How Do You Say "Keep Off the Grass" In A Language We Won't Speak for 1,000 Years?

From Wikipedia:

The Waste Isolation Pilot Plant, or WIPP, is the world's first underground repository licensed to safely and permanently dispose of transuranic radioactive waste that is left from the research and production of nuclear weapons. It is located approximately 26-miles almost due east of Carlsbad, New Mexico. Waste is placed in rooms 2,150 feet (655 m) underground that have been excavated within a 3,000 foot (1000 m) thick salt formation (Salado and Castile Formations) that has been stable for more than 250 million years. Because salt is somewhat plastic and will flow to seal any cracks that develop, it was chosen as a host medium for the WIPP project.

Waste that is to be disposed of at the location must meet certain "waste acceptance criteria". WIPP is unsuited for high level radioactive waste as its high heat attracts water which would lead to rapid corrosion of the waste packages, and the dissolution of the waste into the salty water. The containers can also only contain a limited amount of liquids. The energy released from radioactive materials will dissociate water into hydrogen and oxygen. This could then create a potentially explosive environment inside the container. The containers must be vented, as well, to prevent this from happening.

Because drilling or excavation in the area will be hazardous long after the area is being actively used, there are plans to construct markers to deter inadvertent human intrusion for the next ten thousand years.

• Here's the formal report on these "keep off the grass" installations.