Hello and welcome to BYC, You found an Awesome poultry Forum to be a part of with many great knowledgeable members who are more then willing to jump in and help you with any questions you may have.
So sorry for your loss. The fence helps them get used to each other before they join the rest of the flock. There is defiantly a pecking order and if the ducklings are to young and too small in size compared to the others, good chance they will get picked on. Best of luck and please keep us posted.