Well... small branches etc work... but if it's round and smooth then it doesn't really work.

I don't have oak, but cherry (stones) doesn't work. i would also say rather not.

I don't think so. But there is such a thing as a wire ball on a style. You simply push this device over the surface or meadow; the wires separate and pick up round objects (plums, apples, nuts, etc.), which then remain in the "ball". Unfortunately I can't give you a supplier, but you can find a view at https://www.amazon.de/Feucht-Obs....
Good luck and greetings! Peter