Floor beats diaper any day.

Kid has been asking and actually peeing in potty for maybe half a year now. Taught him to take his pants and underwear off before doing his thing. He even has learned to control his urges for a while (meaning, that he could ask for potty and actually hold it in for some time, up to maybe a couple of minutes).
This week he has started to pee in his pants. I blame myself and local swimming pool. The thing is, that they have a playroom, which we visit after the swimming session, so he can dry down a bit. Playroom is located outside their "paid zone" (pools, slides, dressing rooms and bathrooms), which are gated off and accessible only by using key+token provided. So it seems, that once you're out, you're out. Since kid swallows a lot of water during our swimming practices, he pees often and a lot afterwards. So, to avoid him peeing himself and then going home in winter (it can hit down to -30' C around here) with wet clothes, I put a diaper on him. And every time he asked for potty in the playroom, I explained, that there's no potty available and you have a diaper so you can pee in your pants. Apparently, it stuck. Now he just pees in his pants even at home when he does not have a diaper. Damn, that's one huge step back.

Morale of the story: once you have thought your kid to go potty, don't revert back to diapers. Let him pee just on the floor, or teach to hold it in for a while longer (you'll be surprised for how long they can actually do it), but don't tell your kid "just pee in your pants". This shit sticks.