How to gain more lower Tricep mass?

[MonStar1023]

I read somewhere I think it was Arnold's book that to target the lower-triceps you should perform dips with your elbows close to your body and really lockout hard at the top. I know its impossible to isolate one head of a muscle group but it seems understandable that different exercises from different angles could emphasize a certain part of the muscle group more. Good luck!