I have never thought about throwing rocks in to try to flush the bird.
In the first pic the thistles and other weeds conceal a large, deep ditch and a fence behind which is some bushes. I could walk in if it were only thistles but the ditch and fence pose problems.
The second pic shows bushes and I could not push my way very far into them and could not swing the gun to shoot among them either. Those bushes extend for about another 30 yards down the hill . I try to deal with this sort of problem by not going to the dog . I look for easier walking off to one side of her or the other that might offer a shot at the bird then send the dog in to flush from as much as 20-30 yards away. It doesn't always work and maybe 2 out of 3 times the bird exits where it cannot be shot..... but the third time makes it worthwhile !
That is what happened in this pic. The vizsla went on point to a pheasant down in the bottom of a very muddy sided little gulley full of fallen branches and a few trees. I commanded the flush from the top of the gulley , she flushed the bird and this time it was shot.
I wouldn't have liked going down into that gulley to flush the bird or even to tell the dog to flush it.
Bill T.