My daughter (20 months) does the same thing all the time. At least for you it's only pee in the crib so far.. I had to deal with constant finger painting with the other stuff. Gross. She can undress herself from most anything..overalls, the pj's with the snap collar, etc. If she has an easy outfit on, she will even take the pants off, take the diaper off, throw the diaper behind the crib and put her pants back on.. so I can't immediately tell that she isn't wearing her diaper. The only things she can't get out of so far are like the other posters said..pj's on backwards so the zipper is in the back and snap crotch onesies (I know those are next though, she's close..has gotten two of the snaps undone so far). I have no idea how to help you other than to hope that it's a phase and dress her accordingly in things she can't get out of. Most days I don't even bother getting her dressed unless we are going somewhere since she will get naked while playing also and I don't feel like changing her to the pj's for naps. Reasoning with her doesn't work, at least not yet..I tell her that's "bad" and she tells me "no". So you're not alone.. good luck!