I have a toy terrier in fact i have two recently rehomed and they bark and chase anyone who leaves or arrives  at my door the male of the two was castrated recently and he actually bit my friend who stays in my house  as she was leaving the garden and later  the same evening he went for me  on my leaving the garden what can i do i cant put up with this sort of behavior

To start with make sure they are either both on leads when you answer the door so you can stop them doing their own thing, or secondly shut them behind a door in another room when you need to answer the door (you can train them so that whenever the doorbell or knocker goes they go to that room to make things easier).
Then you need to discover *why* they are feeling they have to defend you/your property........  They may be scared, one may be winding the other up, they may not feel you are dealing with it properly - diagnosis of this without being able to see the dogs is difficult and it would be worth your while contacting an experienced behaviourist to get your dogs assesed.