I have a little experience of similar, although I was not the trail builder. I’m linked to the landowner. In our case the starting issues were this and a question of users ultimately securing new legal rights which might affect value or inhibit other things the landowner might want to do later, eg a right of way or “village green” type rights. However different landowners may be very different and if there’s nothing in it for them, or they’re just busy, I’d expect many to be uncooperative regardless of the liability issue, or at least disinterested in spending time getting themselves comfortable with it.
There are IMBA documents on the net that cover the liability issue including an American one which was helpful even if in a different country. I felt they made a decent case that a law suit was unlikely if the owner and builders had done the right basic things, however a lawyer was advising that the issue would never entirely go away if the activity continued.
For what it’s worth, the folk I know bought the land, the riding and other activities have continued without any landowner issue and I don’t think the trail builders are organised together or have approached the landowners.
