The only way flukes can ‘reappear’ in the pond after eradication would be if the larval or embryonic forms were not eradicated in the same process (at the same time) as the adults, or if you introduced new fish as carriers of new parasites. They don’t just reappear naturally as has been asserted by some misinformed. In fact, flukes cannot sustain a natural population without the influx of new fish. So, once they are really gone, they are really gone until or unless you get a new infected fish.

The most common cause of reinfection is FAILURE TO CHECK to make sure your initial treatment is 100% effective. So, after you treat Flukes "full course" check once a week for a few weeks after to make sure they "stay gone"

Your microscope would be handy for this and is easy to use.