Can i stop my son's biological father seeing him ?

my sons biological dad saw him up to the first year ( he is now 5 ) and then started interfering with his routien and as he couldnt get his own way he stopped seeing him altogether and took me to court and tried getting the access he wanted . after a few times at court he decided to completly give up saying i was telling lie etc . now 4 years on i am constantly being black mailed and he has gone out of his way to find where i live and the car i drive to pester me constantly - i just cant get him to leave us alone . he is now saying he wants access again . but i dont want him to have any access at all due to the fact he is a alcoholic he takes hard drugs and had frequently frightened my little boy in the past to the fact he is now actually scared of him . my son does not know his real dad and referes to him as dean (his real name) . im in a secure relationship and have been for 3 years and i really dont need his dad back in his life making a mess of things . my child has also recently started primary school so i dont want any interference . please help on my rights to this ! my solictor is usless and wont really say much as she never beleves he will go to court . but i just want my mind at ease ..