If he's still defensive after 4 months, it's time to look at a few factors:

1. What is your husbandry setup?
a. Tempuratures, hot and cool side, moderated by a thermostat?
b. humidity
c. hides
d. substrate
e. etc.

2. What size prey are you feeding him, and how often? If his prey's not big enough, he could simply be hungry.

Pictures of both the snake and his environment would help. =]