IMO, I think it is consistancy...
Make sure and explain before bed, go pee, have a drink ( maybe put a small dixie cup on night stand )
Then, when he gets up, say nothing but "it's bedtime."
when he gets up again "it's bedtime"
on and on and on and on...

but the key is to say nothing else, don't get angry or frusterated, that is what they want ( attention)
if he has a nap during the day, prob cut that out, he might not be tired.
We go through this with my dd and honestly, you give her an inch she will take a MILE for the next week...