Soil...... My soil tends to be reasonably tillable. No compact clay. It's real tough to dirt with a shovel because of the constant (it's beyond using the word abundant) rocks, but what soil that exists between the rocks consists mostly of sand and loam. Although I have no experience with it, I suspect that hard pan clay would be a challenge for even a pig.
Rock.... Part of the rock I deal with in the top 12" of soil is carry-able size. So my pigs can lift and move anything smaller than a basketball. But there are areas where pahoehoe lava forms the base, so there is nothing that the pigs or even a backhoe can break up. Pahoehoe lava is like working with a concrete pad. One needs a hydraulic hammer to bust it up.
Pigs.... My pigs have strong long snoots and a desire to root. The current two pigs are proving to be my best rooters to date. Not all pigs get into rooting like these two guys. Some pigs seem to just like scuffling the surface. Certain breeds of pigs have short snouts, which might have a bearing on their rooting ability. I haven't had those breeds, like to Kunekunes or pot bellies, so I'm not sure. My own pigs are a mix of domestic types plus Hawaiian ferals.
Above shows the devastation left behind by the pigs as I moved their portable pen down the slope. Every bit of grass eaten, even inch of surface turned.
One of the hens walking by gives you some idea of the size of the rocks.
I'm getting ready to plant this area with something in order to try to out compete whatever grass tries to grow back. I'm planning on sweet potato. I have a variety that is shade tolerant and produces compact greenery. It's a poor producer of tubers though. Most people won't grow it because of it's poor tuber production. But I find it has it's place for growing in shade and making rabbit fodder for me.
So I'll pick up most of the big rocks. Then I'll top dress with wood ash and rabbit manure. Next I'll plant. I won't try to dig nor smooth the ground out. Not at thus stage at least. In 6 months or so when I get around to harvest the greens, I'll gradually smooth the land and fork in horse manure. There are not much in the way of veggies that will produce in this amount of shade, so I'll most likely keep this particular area in sweet potato greens for the livestock.