[Closed] shooting nuisance pigeons - technical question

there are pigeons in a tall tree above my garden that, of an evening, like to recreate the Somme in the decked area with their multi-coloured scatter-gun droppings.
the only way I can see of getting rid of them is to shoot them down.
the legalities, as I understand them, of shooting stuff in my garden is that it is fine as long as the pellets don't leave the boundary of the garden.
so, technical questions are, can I be sure that if I shoot up in the air that 1) the pellets aren't going to land outside the garden boundary 2) that they won't hurt anyone when they return to earth; what is the terminal velocity of a standard air rifle round falling from the sky?