FENCE LINE

Note: It is usual [but NOT invariable] for the fence to designate the boundary of property.

The owner of a fence must ensure that it is fixed within his delineated boundary and no part trespasses on or over his neighbour's property.
This includes any cladding to the post that faces away from the property e.g. any rails to which close board or other types of pale are fixed.
Strictly speaking it also applies to the concrete surround of any post i.e. the whole of the concrete post surround must lie within the owner's property.

Where the face and opposite side of a fence vary in appearance, it is perfectly acceptable for the fence owner to have the better face facing his property.
The strong held belief that the owner of a fence can be determined by the way the 'best' side faces is fallacious.
It is only the deeds &/or Land Registry that can identify the boundary line.