It was my crested pekin and my heavier welsh harlequin that had foot issues. My other 4, a lighter bodied welsh harlequin, a slim cayuga, and 2 khakis didn't have problems. When I switched to grass (and also removed other hard things from the environment) the foot issues went away.I was worried about that as well. I actually bought a ton of sand just in case the pea gravel didn’t work out. The setup would work with either with minor modifications. So far I have not had any problems. What kind of duck did you have?
I'm happy to hear you aren't having problems!