I dont, and have never carried any form of written permission with me, when carrying out pest control on any of my permissions.
That includes shotgun, rifle, trapping and ferreting.
I have also, never had a time when I wish I had been carrying a permission slip.
I will probably get slagged for this, but I am a firm believer that how you dress and behave when out with your guns, will either draw attention to yourself or not, and may result in a phone call to the cops or not. In the community I live, most people will phone the landowner if they have concerns, and not the cops.
I