[simpleguitar]

500 years is not children of your grand children. If people still have children at 30, your "children of your grandchildren" would be born only 90 years after you, and even if they live to 90, that's only 180 years.

Doing the same math, the 90 year old that sees your web page 500 years from now would have to be born 410 years from now, and at 30 years per generation, that's 13+ generations. At that point, this descendant is related to you as much as a you are to a random stranger from your city.

Look around and see what lasts 500 years: tombstones, statues, family heirlooms.

Your best bet might be to create a ritual, and have your children practice it as part of a religious ceremony!