Tinyliny gave great advice.
The only thing I'd like to ad is offer him a little more chance to read your body language before asking to whoa. Humans aren't aware of the body language they carry, you are asking him to read you but you nearly jump to a stop which brings him a few steps ahead of you because he missed the cue. (It takes less to stop 100 pounds than 1000). So before you slam on your breaks and say whoa, think to yourself "Im thinking about stopping" then proceed with stopping yourself and telling him whoa. This will give him the proper cues, your body will do tiny changes because you are thinking about stopping. I am sure you'll find he will stop before you say whoa.