So I figured maybe someone on here had
experience measuring the required ground..

Well, not a lot of experience, but the keywords you're looking for are
"fall of potential".

Depending on which spec you're meeting, you drive multiple ground rods
in at distances that are large compared to the length of the rods.
Then you measure the resistance between the rods.

Just sticking your ohmmeter leads between two ground rods is not good
enough. There is a substantial chunk of 60Hz AC and probably some DC
current flowing in the ground and the little battery inside the
ohmmeter will generally add nothing. Fall-of-potential meters use much
larger currents (and usually measurement techniques, like using an AC
frequency unrelated to 60Hz and harmonics) to overcome this.

My impression with antenna installations that I've been peripherally
involved in is that NEC requirements (25 ohms) are generally easy to
meet unless you've got dry rocky soil. And that the 25-ohm requriement
is nowhere near good enough to protect your equipment/buildings from a
direct hit.

Tim.