The issue with an 8' rod is not because of the exposed part might be damaged, it is because code states it must have 8' in contact with Earth 250.53(G).
I agree...that's what the code says....but here's the Catch-22:
If a guy buries the rod 8' [thus the acorn is below grade] then an inspector wants him to dig it up to see the connection...so typically [in our area] the ECs leave the rod a few inches above grade [as long as it is protected from damage] so they are not hassled by the inspectors.
In our area it is common for a replacement/ service upgrade to be done in one day...EC calls for inspection and has homeowner stand the inspection...these are simple jobs with not a lot that can go wrong....they leave the rod a couple inches above grade for inspection purposes....job is done....signed off...and they don't have to stand the inspection or return [1 day in-and-out]....if everything goes well [no violations...other than the 2"]...job is done.
As an electrician I install rods below grade and have it open for inspection and stand the inspection...but since the above is common practice, as an inspector, I don't hassle the EC for leaving it above grade.