How about fertilizing the pond to get an algae bloom and reduce visibility?
Trout might dislike turbid water...
EDIT:
About the mesh size. Sure, the less, the better but it might be bad for your fish (trout is such a vulnerable fish and getting it in the net is not an option).
My experience shows that 80 mm is only for large fish and could be good for your case. In my ponds such net can be useful for common carp only and from ~1,5+ kg (even these fish can be taken out easily). Shouldn't bother your trout.
60 mm probably won't hurt your trout either.
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You know gill net prices in USA and you better decide the amount of nets you can afford. Here in Latvia it's possible to buy chinese 90 m nets for ~12 USD (poor quality but could be suitable for this case). I guess that you probably can order them somewhere on Internet.
I'd recommend to start with one net only, just in case.
