Hmmm, good point, I have thought about this, possibly multiple people claiming the same duck(s). The best I idea I have so far is to require racers to leave a comment first on the race post and claim the ducks, then send the HBD with memo after. I will have to emphasize that all racers check the comments section first to make sure their desired duck hasn't already been claimed.
The new PeakD chat feature may be a useful tool for coordinating and keeping things organized too, I should integrate it into the race somehow.
Like you said too, if there is duck confusion it should be easy to solve because I will initially only do a weekly race, and this will allow for 7 days each time to iron out all the kinks and problems. When we have a well-oiled machine and the system seems to be user-friendly, perhaps there could be daily races, that would sure be fun for me and the kids.