I currently live in a community with private horse trails that back up to my property, arena and a large field that is fantastic for riding in. We all pay into the maintenance of the trails and thus are allowed to ride on them. Recently the neighboring community that does not have their own trail system has been coming over to ride our trails and use our arena so the whole perimeter has had a fence set up to close off the trails to anyone not a member. This choice wasn’t made out of wanting to take away riding space from other people, but to help protect ourselves in the event of an accident. No trespassing signs and fences go a long way when insurance has to get involved in an accident.
Currently, I’m looking into moving out of the community to go back home and plan on getting 5 acres. Unfortunately, the property I have my eye on doesn’t have any trails connected so my best option will be trailering a few miles away to a local forest preserve. I would never dream of riding on my neighbors properties, unless they offer permission, and have accepted that moving means I won’t be able trail ride as easily. It’s one of the tradeoffs of having your own horse property as it’s less likely to be connected to a trail system.
Personally, I would set up your fences and no trespassing signs. Check with your insurance to ensure that’s all they require, and just let your neighbors know that because of insurance purposes you cannot allow riding across your land. If you wanted you could set up an “easement” along the back of your property as a trail but I would speak with an attorney and your insurance before doing anything of the sort.