I would agree with Efjay - at daycare there would be expectation that he goes when requested at certain times of day. We have children we know need extra reminders and so we ask them to go throughout the day apart from regular toilet times.
I would give him clear expectations explaining as you go, 'yesterday you wee'd your pants when you forgot to go to the toilet, so I want you to go when mummy asks you to so that doesn't happen today' kind of thing.
As for punishment regarding tt, nope, I wouldn't. However like others have said, I would expect him to help clean up when he does have an accident. I've done that with the 5 year old 'can't be bothered holding on to my penis' boys at work who handsfree flail it everywhere and consequently wee on the seat (cause they fail to remember to lift it) and floor, with gentle explanation that the girls don't want to sit in their wee and no one wants to stand in it either!