Some posts i've read, some carry a hammer and a rod or large nail or railroad spike. And drive into the ground to break up the 1st two or three inches. Good luck HH
You may want to try one of those rock hammers. They sale them inn most hardware stores... Or you may even try one of those roofing hammers that have the flat blade for chopping. I know that sandstone ground is some hard digging. You shouldn't have too hard a time with either of those hammers though... Just be careful not to scar your finds...