"Any one have experience with this "type" of stake in rocky soil?"
Yep. And I confess pounding them in with a big rock. Relentlessly, until they are solid.
So I've destroyed the nylon heads, and separated the aluminum tips. Then I moved on to Easton Aluminum. But truth be told, those heads will also come off as a result of hammering.
So, be gentle my friend.
[Ya, I know - "lighten up with the rock" - but at dark-thirty and time running out, I'm looking for a big rock.]