I just got loads of permission by calling round on farms and just introducing myself and stating I do a bit of ferreting and I'm after a bit more permission? I got a yes straight away, plus they put me onto new farmers, i think it does help when I go in my works gas van?
I think first impressions do make a difference so dress accordingly, like no cammo, or track suits, just plains clothes
Also try calling in with the family in the car to show you're a family man?
Hope this helps
Chris