Four year old holding poo and wee

[Struggling_30]

It's been going on for years now. He has a great diet and has never been constipated but holds. He currently has one child's movicol most days but is so good at holding. He wees himself when he needs to poo and has now started to hold wee as well when he doesn't need to poo. He uses a potty at home so he's in a better position. When holding poo he will smear in his pants. He's at school now and has started to wet his trousers. I just don't know what to do.