My daughter started doing that, as well, a few months back. My husband and I came up with an easy cheap solution. We bought 3 yards of a netting material at Wal-Mart (which was around 70 cents a yard). Then we placed it over the top of the crib railing, so that it hung over both sides, and the ends were at the bottom of the railing. Then, we pulled everything tight, and my husband zip-tied (although, if you don't have those, I'm sure you could find some string or something that would work) along the bottom of the railing and the sides of the top. It works out great! No more getting up in the middle of the night 5 times to put her back in her crib. It's probably the cheapest, safe solution you'll find. The netting allows them to breathe, even if they get right up next to it, but there's nothing in the crib that won't let them move, and, therefore, makes a mobile baby frustrated. I hope that helps!