If the pond is only 75 yds. long and you' re in the middle you should be able to get a decent 30-35 yd shot to the end right. Maybe take some heavier shot with you so you can shoot a little further.

If they' re getting by you on the way in they should be taking off in another direction. Maybe you could convince them to take off towards you. Take a sling shot with you and after the ducks land shoot a few rocks into the weeds/water on the other side of them, maybe that' ll scare them towards you on take off and close enough for a shot.