My mallard, Peep, has always kinda kept herself away from being in the flock. Her offspring, mallard x pekin, also get cases of the wanderings... They seem to be explorers! That being said, I don't do anything about it, I don't have to. If you do have to fix that, the wing clipping you've done and only let them roam befor you've fed them and use their food to bring them back. Of course this all looks good on paper... In ducks world.... Begging and bribery with some pleading and shepherding thrown in!