Take a deep breath:
Yeh, I had trouble with those pesky blighters (exploding stones) while putting together that Ben McDuffy thingy, even though, like yourself, I had Blend as Stone Density unchecked. I'm sure my problem was having very small scale displacement on my grass (power fractal displacement directly below my stones (above it on the node list). This is all in the shaders group, you understand. I think the problem arises when you use a Distribution shader to Slope constrain the stones, and have the Slope key set to Final normal. That setting picks up any small displacements you have immediately underlying your stones, but after the Compute terrain at the bottom of the Terrain group. Aha, I said, ahaha, I'm gonna bung a sneaky wee Compute terrain between the troublesome grass shader displacement and my stones. That'll sort it out. No it bleeping well didn't. If you then change the Slope key (of the Distribution shader for your stones) to Final terrain you are then picking up displacement info from the Compute terrain at the bottom of the Terrain group. But, because I had some severe displacement in the terrain group I still got some exploding stones. My stones stopped exploding when I changed the Slope key to Planet/Object normal. Of course they stopped exploding, the planet being flat (well flat in a spherical way, not in a flat earth way) before adding displacement, and therefore negating the need for a Slope constraint. Sheesh; in the end I don't know how I got rid of those exploding blighters. You know what, I think I just got lucky.
Ok, you can let your breath out.
Btw; DO let me know if the above sounds like a bag of bollox. Or, perhaps you found a smidgeon of sanity in the above stream of consciousness rant.
John
