Pekin Pond Problem: Leeches

Hi Guys,
My 4 pekins are about to be 7 weeks old and with the weather finally warming up in Michigan, we've been having them free range. For the past 2 weeks, they've been in in out of our pond and now as soon as I let them out of their home in the morning they make a straight run for it and don't come back to our little beach area until I get the peas and call them over. My worry is that the last few days they have had a few leeches on their legs and little webbed feet. I know they are a predator to leeches and love to eat them but I just wanted to make sure I am not harming them in any way by not forcing them to come in while I go and grab the salt to get the leeches to let go.

My fiancé had mentioned wanting to put some salt in our 2 acre pond to get rid of the leeches. Would that affect the ducks?

Lastly, and a little unrelated, we've had them since they were a week old and while they always quacked when we picked them up. It seems as while they get older they are afraid of us more and more. I do my best to give them treats and often sat around them when they were little but now they just run for the pond and although they come when I get the bag of treats and they'll eat out of my hand. Is there a way to help encourage them to get used to us?

Thanks for your help,
Jamie T