Hey Mike,
My question on the studs was which ones you used that worked so well. I used something that looked exactly like what you posted, that I got in bulk from a liquidation sale from a hotel operator that was going out of business. Super convenient to put into the felt as you just use the standard hex bit holder to drive them in. Whatever metal composition on the ones I used was just not the right kind that will grab hold of the snot covered granite in the park. Mine look like SS, and were finished to a higher standard than your regular fastener, so I suspect that was the problem. Two super hard surfaces and neither one would give to bite. Leaving out on the trip I was all proud of myself for buying 20lbs of expensive screws for $2.
I think the ones that are commercially sold as studs are made of a softer material so that once through the snot, the rock takes hold of the stud. After I posted the question found some aluminum head zip screws that would probably be perfect.