I make the ones out of landware cloth, they are an 8x8 cube and come with 30 balls, it
sounds like a lot, but once they are in the cube its really only enough to cover the bottom, plus a few.
My little fuzz-bottoms have had no problems getting on or out, but it is shallow too.
This is a great warning though!
I will now be adding "escape ropes" to mine. Kind of like a fireman's pole that attaches from top to bottom so they will have something to grab onto if they were to get in a situation like that.