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I think it would not be that hard to calculate the right momentum to spread gravel and sand into the path of a certain kind of satelite. You would have to consider whether to target high or low earth orbits. But you could shoot a payload out against the angular momentum of earth to release debris at the distance of geostationary orbit at the level of the equator and then I think all the geostationary satellites would run in to it in a few days. I think the polar and low earth orbit satellites might have to be targetted separately but the same principle applies— you put the debris in an area which certain types of satellites will all have to pass through every few days.

When you make it up into orbit, you have to be moving at a certain speed in a direction. A direction particular in that you are still falling but you just keep missing the Earth. If you "just sit there" you will simply fall back down to Earth.

Go play Kerbal Space Program. Or read up on orbital mechanics if you are mathematically inclined.