If it is a behavioral and not physiological, you can try this approach.
(My son just turned 5. He had the same potty training issue. Just too busy to stop. Bowel movements he could feel sneaking up so he'd make it to the bathroom. Bladder it was like all of a sudden it hit because he'd been too busy playing to notice)
First, stop telling him when to go. This makes him dependent on you to take him. He needs to initiate it himself. So, the next time he has an accident simply say (in a non-angry tone. Just have a VERY flat affect) "Uh-oh, you pee peed in your pants. Pee pee goes in the potty" AND THAT"S ALL YOU SAY! Very important not to give too much attention as this may reinforce the behavior. Then you take his hand and make him feel that he's wet. Then take him to the bathroom. Pull his pants down and sit him on the potty (for barely a second), then immediately take him off the potty, pull his wet undies/clothes back up and take him back to the scene of the crime and repeat, "uh oh you pee peed in your...." and do this FIVE TIMES. This is a researched based procedure and is used to train children with autism and other disabilties. This part of the method is called Positive practice.
It's not a punitive method but it's certainly not fun (it's not fun for you either so hang in there and just be determined. Five times of pants down, on the potty, off the potty, back to the scene of the crime gets very tiring for mom. but don't let it show!) He's probably think, "man, that wasn't fun, I better remember to pee in the potty because I don't want to do that five times again!) I only had to do this ONCE with my son and we were accident free after that! and now I don't have to be constantly reminding him either. One less thing on my mommy responsibilities list!
A second part you can add is the "dry check". Set your timer for every five minutes (it's hard but will work) and check him to see that he's dry. When he is, praise him and hug him like crazy! or offer another reinforcer you know he'll like. That way you're showing him the behavior you want him to achieve while extinguishing the other behavior of peeing in his pants.
Good luck, let me know if I can help further!
R.