Ground rod....dig a small hole about the size of a 16oz cup. Fill with water and let it soak in. Stab the ground rod into the bottom of the hole, lift it up, stab again, lift up, stab, lift up, stab, add water, lift up, stab, lift up, stab, add water, etc., etc.,. It gradually works the ground rod into the ground. I've put 8' ground rods down for ham radio use using this method. One school of thought says the ground is compromised because water is used, other school says it works fine. It's worked fine for me, ymmv.
Oh, if you hit a rock all bets are off.
I hit one at about 7' one time and figured I would just pound it on in with a sledge hammer....nada. Probably was a rock only the size of a pingpong ball but it stopped that rod dead in it's tracks.
Ed
Oh, if you hit a rock all bets are off.

Ed