Land Navigation (okay: surveying)

I saw a couple of items concerning navigation recently.  One was this Veritasium video on GPS jamming in Europe:

source: https://www.youtube.com/watch?v=tz23G_UXCGA

Those wacky Russians !  The one thing they didn't mention was who tipped off the GPS researcher to the jamming in the first place.  Probably the same one who provided the raw GPS data ?

The other was this IEEE Spectrum article on using magnetometers for navigation:

https://spectrum.ieee.org/magnetometers-hidonix-astranav-gps-alternative

Both are interesting - one thing that I've been interested in as a property owner is just where are property lines that aren't line of sight from the corner stakes that the surveyors drive in.  At one time I looked at DGPS:

https://en.wikipedia.org/wiki/Differential_GPS

But apparently DGPS is gone in the US.  But you might be able to do a local DGPS, say put a DGPS broadcast station at a known point (USGS benchmark or the corner stake of a property)  then you could broadcast local corrections to the mobile GPS receiver.  But it would cost $$ plus a lot of time/expertise to build your own.  

It would be nice to know where the property boundaries are though.  So I will have to see what kind of surveying / property line / mapping apps are out there now - this is a problem that must have been solved before, hopefully for free ?

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm