In my experience, your fence will only partially solve the problem. He will move it. He will do everything to keep your fence from setting the true boundary. And don't bother to go half on the fence. This is war. War is not about whose right, its about who's left. There needs to be a substantial boundary marker that is permanent, indisputable, and easily seen. Yes he will try to move, alter or destroy it. Have a lawyer send him a notice of intent to sue for costs, distress and punitive dmamages. If necessary, follow through. Otherwise, your property has become devalued for you and whomever would be foolish enough to buy it.