[dataway]

Record your land survey at the
county or wherever official records
where you live are kept.

Update your land title to reflect
the survey and record the update.

Yep, first thing is to get your property lines recorded and entrenched in the local government. After that, technically a stake and strings should suffice for a barrier legally. I'd put a camera out there that watches the property line 24/7 and records it on something like a rolling 7 day loop. Lay a line of medium size stones that he would have to move to get around, or concrete building blocks .... anything where he would have to make a physical effort on your property to remove and you would have a recording of it. At that point you could pursue a criminal judgement against him for property damage, trespass etc. Bear in mind the Police will do nothing unless you personally press charges.