Neighbour and Fence issue

[Dijon1975]

My neighbour came to me for 3rd time today evening and we are not agreeing. Immediately he started threatening me that he will build the fence in the common property and make me pay. I said i will not pay and he mentioned that he will make me pay. I asked him are you threatening me and he said yes. I asked him to leave the house before i call the cops.

Now my question is

1) Can he build a fence without my approval in the property line?
2) Can he build a fence in the property line and paint crazy things on my side? (on the property line)
3) what to do in case if he starts the building fence?
4) Can i call the cops if he starts building?

AG