It says "Call before you dig." Banging in a rod isn't digging.
Just as important is to know just what the 811 service represents. Their marking is only 'guaranteed' within three feet either side of the line they mark out. So, if you want to bang in that ground rod, that marking means little. There's almost sure to be something within six feet; they're not telling you anything you don't already know.
The one thing you're most likely to damage is the one thing they don't even try to mark: the sewer line. That ground rod would go right through the glorified cardboard that is used for the sewers. Nor do they identify anything the wasn't laid by the utilities. Just try to get them to trace the feeder you know exists between two buildings!
"Call" was nice when it first started. Call them up, give the address, they were there in a day. Now, however, the only thing they're clear about is "We're the boss and we'll punish you, you serf." Now it's TWO days, and they want all manner of information ... cross streets, endless questions, etc. Are you digging by hand? Are you boring? Etc.
At least three times I've called, had them give me the 'all clear' ... when I KNEW they were wrong. Once it was a buried oil pipeline they failed to discover; another was the main power and communicatin feed to the local airport (their marks were off by half a block); the third was an electric utility high voltage trunk. Let me tell you from experience: it's loads of fun calling them back and telling them that they goofed - now would they kindly come back out and try again? Might as well hire a hillbilly with a forked stick.
Another thing that calls into question all this witchcraft is the fact that you simply cannot call them up and say "I just bought this property, can you come out and mark all the lines, so I know what I have?" Funny, the utilities had no trouble doing just this in the 60's!