Improve obedience

My 7yo knows what I'm asking but sometimes chooses not to listen. I know it's my fault bc I've been too soft on him recently. We've being going hard on sit and down stays with distraction recently bc I'm tired of him getting up from stay whenever he feels like it, but he will fidget and stand up to reposition himself so he can see what's going on better if I walk behind him for example. I feel like I'm constantly correcting him in stays and it's really annoying because he knows what stay means and has a break command.

He will walk at heel perfect until he gets bored/distracted. It's like little things but it adds up especially when we're in high distraction environments which is when he needs it most. We've been working on desensitising to distractions by staying in a down in busy places which is going well, but he will stand up a few times and I have to put him back into down.

How can I improve this? Do I just stick it out with the "no, down stay" correction? He seems to think if hes manages to move he's won the game kinda thing, so the verbal corrections don't feel like they're helping, but he usually won't move unless im in a place where im not able to stop him before he gets up