If hitting isn't working you aren't actually hitting.
Don't nitpick. Either hit him or not. Don't poke.
I would hit him HARD for biting. I would carry a crop, or ideally a lead and pop him for getting in your space. Back him up *and follow him* to push him out of your space, repeat as necessary, BUT make sure to up the ante every time you repeat to make sure he gets the message, no games. As far as dragging I prefer a stud chain, but know some people like rope halters. Definitely a longer lead.
Check out this thread for leading/pushy advice- Haflinger Freight Train...