Lego Worlds: How To Keep Characters Out

I have an area in my game where I do not want characters to come. They oftentimes will steal the vehicles I place, and by when riding vehicles, they often run into things and break the stuff I have placed with the discovery tool. This is extremely annoying!
I tried placing a wall around it, but they seem to spawn inside. This may be because I have a road set up inside. What can I do to keep them from spawning inside? Is this even possible? Any other solutions?