DS is 2.5 and has been dry in the day for about a month. Got the hang of potty training really well and didn't regress at all when he got chickenpox two weeks after starting. The last few days he's had several accidents. Some real, some definitely on purpose. I'm sure this is a phase (he is going through a defiant stage right now to say the least!) 
The question is do I tell him off when he wets on purpose? Or ignore? I've been making light of it till now and we've just had a talk in the bath about where weewees go and why it isn't nice to wee on the floor. I made it clear that I understand sometimes he can't help it and the wee comes too quickly. Any other tips?