Round here on the edge of the moors you will really struggle with plastic deeks and a pigeon shooting type net hide. I build a hide in place with nets, pallets, branches even old farm machinery a week or two in advance. Then pick a windy over cast day and use flocked decoys, the next time I shoot I will use dead birds then change to a dead lamb with 1 bird on a floater in the wind then next time maybe use a call....you have to keep trying a new approach as you wont fool em twice once they have seen/heard someone shooting in the area. The main thing I find is a good hide spend a good afternoon building hides in different areas, plenty of branches over the top of it. Sometimes I'll try and be in a crow hide before first light as well.
Iv decoyed crows on arable fields and they were much easier than these wild things on the lambing fields, you will never shoot 80 of these.