I am fortunate in that I know a lot of farmers and as my friends will know I am not afraid to strike up a conversation with any landowner or farmer anywhere and it has worked very successfully in the past and hopefully will well into the future, if you are honesty and make a good representation to the farmer then you have every chance of getting his permission, I have previously arrange digs for clubs where up to 60 people have turned out, i charge them £5 a head which is often donated to the farmers nominated charity and a receipt raise in the farmers name, this is given to the farmer and he gets the money back through his taxes, the issues that tend to come up is when someone fails to declare their finds, or people leave holes or big pieces of plough shard on the top of the field, it is about showing respect, how would you like it if a bunch of strangers left all their yoghurt pots banana, empty drinks bottles in the hedges around your fields, silly things like driving across the field because you cant be bothered to walk over upset farmers, Most people have a home and a place they work and friends family etc. which are all separate, farmers have their farms it is there world most spend every day working on their farm or out in their fields tending animals or crops they can go days or in some cases weeks without contact with anyone else apart from other farmers and family members so it is in effect a closed system, all of a sudden they get one or a small group of Townies turning up wanting permission to search the land, appearance is a lot tattoos piercings etc. do little to impress or endear you to a farmer who experience has taught him Townies steal no not all of them but enough to cause farmers to be apprehensive about letting groups of people on to their land, you have to win them over, it took me 3 years to get on to one of my permissions, so keep trying and don't give up