I made a Whopper Plopper with a metal tail fin, painted to imitate a juvenile red wing black bird.
It swims, but it doesn't have the same plop, plop sound as the original, or my PVC tail version.
I'll be tweaking it to see if I can add a lip to the back edge of the cupped tail, to create that plopping sound.
I also don't like how it hangs at a 45 degree angle on the pause. I had hoped the silicone skirt wings would be up at the surface on the pause. That may require a return to an all PVC tail, for the added buoyancy.