In AG, it is implied once you plant or work the ground that it is yours for that year. I'm under the impression when he stated that in court, he had agreement with your neighbor and disputed ground (he assumed incorrectly) belonged to your neighbor. So he would have no agreement with you-he didn't see need for it. Then again, he might just be a giant jerk.
I'd state in letter that court ruled in your favor. The surveyor has marked the boundaries clearly. He has no permission to be on your ground. I would allow him to finish out the year or until I put up new fence. IF he complains about the seeding, fertilizer, lime, etc, tell him sweetly, need to take that up with neighbor who rented you MY ground. IF he threatens to kill it, then inform him that is vandelism and appropriate authorities will be called.
IF you want to rent to him (I wouldn't) that he can contact you or your contact person.
Sorry for novel.......