The ones I tried with double-sided adhesive tape came apart very
quickly in the water. I did try to coat the edges of the flies with
epoxy, but it obviously was not enough to waterproof them.

One may also make the "spoons" up first, just spread the epoxy on the
thich paper, or card, and complete the rest later. If you use nail
varnish, glitter, etc ,then you don´t need the metallised tape.

Now, I use my own fingernail patterns, as they are easy to make, and
very successful.

TL
MC