Check your policy. Our policy covered the land.
After people started building nearby I started thinking about getting an Umbrella policy. After our car accident, which was not our fault, I bought the Umbrella policy and increased our limits on our car insurance. A car accident that is your fault could really mess you up financially.
I don't remember the exact cost but the Umbrella with 2 or 3 million dollars of liability coverage was not expensive compared to loosing everything.
I sometimes mow our private road that is owned by the land owners. Some of the road is mine. Some theirs. I also grade the road from time to time. I want coverage, especially with mowing, in case something happens. I am real careful with mowing and I don't do it for them often anymore but it only take a second for something bad to happen. The consequences of that one second Oh S...t can last a lifetime.
The best thing you can to to protect from trespasser liability is to post the land in a legal manner. If they trespass and get injured it will be hard if not impossible for them to sue successfully.
Later,
Dan