Several suggestions. Does the town own any land that they keep open – not playgrounds or playing fields of any kind, but land in an open space program, or perhaps there is a land conservancy in your area. Either will do. We had a 47 acre field here, owned by the town and they take hay off it once a year. I reached out to the town council by letter and was turned down several times, but kept at it. And in that letter I described sheepherding as a passive use of land. In fact sheep on a field is the personification of open space. Now I have permission except for the few months the hay is growing.
On a private parcel, Mark’s idea of contacting your hay dealer is excellent. Or if you see a field you like, a letter might work as well. I got my first field by putting something in someone’s mailbox. However, I would also knock on the owner’s door. I would like to meet them and have them understand that I value their property as much as they do. That I am not moving there and when I come, anything I bring with me, leaves with me.
In both cases, you may be asked how often you will be on the property, for how long, how many people. Assure them that the endurance levels of dog and sheep keep the sessions short, that you are not coming in inclement weather as you do not want to damage the field (rain, snow), and that you will not be there when the grass is long because you can’t see the sheep or dogs anyway.
If they ask for insurance, check with your homeowners insurance company. You are looking to get a certificate of liability on your homeowners policy naming the property owner and releasing them from any liability due to your actions.
Having done all this, I do not take dogs to these fields that are not under complete control and I do not take challenging sheep. I want sheep to work and sheep that will load. My challenge is an open field.
Hope this helps.