Welcome to BYC!!! Oh yes, your ducks will get used to the harness. Be certain its light weight, and doesn't try to creep up under their feathers, they won't thank you for that problem. I suggest you give it time. Heres what you do.
1. Put the harness on for 30 min 3x a day for 2 days. (if they still can't ignore it, add on a day or two)
2. put the harness on for 1 hour 3x a day for 2-3 days (like step one, don't move on until they've adjusted again)
3. Put the harenss on for 2-3 hours 2x a day. (once a.m., later pm) don't move on until ducks are totally ok
with harness, and don't freak out even when your putting it on. This may take a few to several days.
4. Once ducks are ok with harness, get some favorite ducky treats (like kale leaves, or whatever you give them)
Put the lead on the harness and let the duck just hang out and relad for a few minutes, then offer the treat a
couple of steps in front of the duck. When he comes, let him have it. Do this a couple of times and then take the
lead off. This is classical conditioning. The duck does what you want, and you give it a postive (happy treat)
reinforcement of the act.
5. Contine doing the treat excercises, until the duck associatiates the harness with pleasent things. Now when you go out and clip on the harness for excersions, offer a treat. Offer another toward the end of the walk, and as needed in between to keep the duck(s) feeling postivie. Remember, ducks are a bit more flighty than chickens, so the training will take longer, but it will work out. Stay after it!