The audacity? Really? That’s a little extreme, isn’t it? I mean, they bought property in an area of little farms, where people have horses, and they see a neighbor riding across your unfenced land on his trail rides. It’s not a big leap to think that they might assume that it’s acceptable to do so.
Especially if they came from an area where such behavior was common. I used to live in an agricultural area in PA and no one minded if you rode across their property as long as you stayed out of the corn fields. We also used to ride on our own hay fields all the time. Heck, at the place I board now, we all occasionally ride around the edges of one hay field and across the middle of the other. Even the owner. It isn’t perceived as a big deal.
So, again, not having been told any different, and having seen your other neighbor ride across your property, it seems perfectly reasonable to me that your new neighbors might believe that it’s an acceptable activity. It seems a bit unfair to work up such a sense of outrage before you’ve explained that that isn’t just a big vacant field of grass, it’s being cultivated for hay, and asked them to stay out of it.
If they continue to ride on it after you’ve asked them to stop, then you can get all mad.