I used to rely on rocks (most of the places I go to have trees). One day in my wanderings I found a great lunch spot: a picnic table on low bluff with a tree overhanging salt water in Tasmania, just right to hang a vertical dipole for 10m. Except that I couldn’t find any rocks: everything was sand, or sandstone that crumbled in my hand when I picked it up. In my searching, however, I found an old sock and filled it with sand, which worked just as well.
Well, not quite as well… A bag of sand or small rocks doesn’t bounce off the tree the way a rock or weighted ball does, instead losing momentum that can help pull the weight back down. Sometimes that’s the only option. Now I might carry a tennis ball with rope attached, and a slit in the side that lets me fill it with local materials when I can’t find a rock of the right size.
I’d also choose braided mason’s twine for the throwing rope rather than paracord - it has a smoother finish, and the weight comes down easier.
I still carry a chalk bag for throwing, however: I put the rope in it, and it comes out with a minimum of tangles.
The vertical radiation patterns of antennas on hilltops are not easily modeled, however. They depend on the steepness of the slope and the distance to the edge, and other details of topograghy. A low dipole near the edge of a steep slope (or, even better, part way down it) can give a good low angle of radiation. (See Moxon’s HF Antennas for All Locations.) But it isn’t the same as a dipole the same total height over flat ground. Being close to the edge of a steep dropoff is often better than being at the highest point of the hill, especially when the top area is relatively flat. The HF Terrain Analyzer (HFTA) software helps, but often the terrain data is too coarse to model it accurately, and it doesn’t account for reflections from sloping hillsides that are off of the path being analyzed.
And, yes, you can be too high above sloping ground. My friend lives on the side of a hill and put up a 4-element 20m yagi on a 55m tower. It worked very poorly. When he analyzed it with HFTA, the problem was that the angle of maximum radiation was below the horizon, and his RF was being reflected by the next range of hills. It turned out that 17m was the optimum height for the slope of his hill, and a 3-element yagi on top of his barn works much better.
So it isn’t as simple as it might seem. Of course, it also depends who you are trying to work: for stations out to a 1000 to 2000km, it isn’t as critical. Trying to work the East Coast of the US from the West Coast on Field Day (~4000km), we need all the low angle help we can get.
