In order for your neighbour to claim adverse possession (AP) he would have to satisfy two requirements (1) uninterrupted factual possession of the land for the requisite period (10 years for registered land and 12 for unregistered land) and (2) an intention on the part of the the neighbour to possess the land during that period of possession.
There must be a sufficient degree of exclusive physical control over the land. What is sufficient will depend on the circumstances and, in particular, the nature of the land and the manner in which land of that nature is commonly used.
Therefore it would depend upon the length of time the neighbour had been possessing the land and if during this time his intention was to possess to the exclusion of all others.
To prevent this you only need to resume possession for a very short period of time to interrupt the neighbour's possession. However, there must be an act of interruption which ends the neighbour's exclusive possession, rather than an act which simply challenges the neighbour's right to possession.
How has the fencing been erected? Do you still have access? How is the neighbour using this land? How long has this been on-going?
The neighbour is committing a trespass by entering the land.
You can exclude the neighbour and block the access. You could write to the neighbour, assert that it is your land, back this up with a copy of the title, you do not consent to the neighbour using the land. You can offer the neighbour a licence to use (in return for a licence fee) the land if the neighbour wants to use it and inform the neighbour that continued use without permission is a trespass.
I hope this is helpful.