Unwelcome mallard

Three mallards generally come and mess up my little pond in about March and they have been coming here for about 3 weeks now. I am not amused as they make such a mess. I go out and chase them off if I am in, but I am sure they just wait for me to go out and then return!
maybe a shot gun is the answer but thinking about that I could never pull the trigger! I keep telling them they are NOT welcome but it makes no difference.
On a different topic -- does anyone else make such a mess making mince pies?! (see my extra)