Hello i am a solicitor with 20 years experience. i will try to help you with this.
I take it you do not have any kind of written right of way. In the absence of that the only way you could have acquired a right of way is through prescription (ie by passing across his land as of right for a long enough period to establish to a right to do so). The period for this is 20 years of continuous and uninterrupted use by you or you predecessors in title.
Your neighbour can not put posts on your property though and you could legitimately insist he remove it from your land.