if they were going on to farm land the chances are they will stop once the crops start to grow as they won't be able to settle but if going onto grass, playing field etc then this won't happen.
Do you leave your birds out? If so you need to get more control over them, keep them hungry, let them excercise and then call them straight back into the loft for food, they will soon learn that once they have excercised it will be food time and won't bother going off.
Phil