There is a technique that might be interesting and not "far future" (currently we can only show a proof of concept, we have not tested it, but it's not far of the "self driving cars" future).
The bigger problem with a message that needs to outlive ourselves is that it needs to "stay alive": as in, it needs to not be destroyed.
To stay alive we can quite literary just do that: either make a robot that is self replicating and intelligent enough that it knows how gather supplies to make multiple copies of itself which.
Or even simpler: encode the message as a DNA sequence into the DNA of some species, many virii actually carry "information" about our history this way. And if you can encode it into a strong bacteria like the cyano bacteria it's probably going to last for a 100s of million years.
