I rent half of a duplex. The other renter continues to trespass on my side of the property line. (no fences).?

The renter on the other side of the duplex I rent continues to encroach on my side of the property line causing damage to trees and the grass. He has installed a clothes line on the property line ind comes on my side to hang clothes. The grass on my side no longer exists. It is dirt. His side of the property is in shambles. The landlord does not want to "get involved". What can I do?