[Duck Butter]

Have a wooden frame cage with hardware cloth that we put critters in but it has a hinged lid that opens out. Whenever you put more than one in there the others sometimes come out. Need an idea on what to put for a lid or an opening so that they can't get out. I have seen some cages built for frogging that you can put the frog in there and he can't get out. Any ideas on this? Thinking maybe some hard plastic pointing down where you can slide your hand in there but be able to get it out. Thanks in advance.