I'm seeing a lot of posts stating something like, "any idiot should know not to dump on your land" etc. However, in many states, under law, you have to post signage or build a fence to notify others of your property boundary. You may be able to prosecute without these things, but it will make your life easier if you clearly mark your property boundary. This usually corresponds to hunting regulation, but in this case I imagine it applies to dumping.
I'm not aware of any States require a fence (although it is a good idea),
some require a paint mark, or
some signage. I'm not a lawyer, look up the law in your own area.