What can I do about my neighbours obsessive behaviour, the main question is about the boundary fence.?

The criminal damage is a police matter and any video evidence that you can get could prove a case of harment against you, if you could try an get a copy of the plans to your property the boundaries will be shown and your neighbour must accept that you have the right to put your fence along it, the Citizens Advice Bureau has free legal help from a solicitor normally on one day in the week, you will need to make an appointment but they will guide you through what you need to do, I hope that you can get this sorted, I would imagine that it is not nice to have these types for a neighbour, I have been very lucky, I have always had good neighbours.