Is the property fenced or have some other clearly defined boundary (ie; fences + canal, waterway etc that defines the boundary)?
If so, than the Inclosed Lands Protection Act would apply and in that case, the Act supports what Rod has pointed out, in that the "owner, occupier or person apparently in charge of those lands" holds to power to order someone off the land. So unless you are the person in control of the land, you don't have the power to order anyone off it.
I would therefore think that the same applies in civil jurisdiction and as such, you don't have a case.