Marianne,
 
I used to have the same type of cage and my little ones figured out how to
get out in no time at all.  The problem is the lack of hooks on the sides.
My boy would push the top up with his head making a gap between the top and
side of the cage, Then he'd grab the top rung of the side, put his head
through the gap, and pull the rest of his body through.  The top usually
came unlatched during this proccess allowing my girl to escape also.  I
solved the problem by securing the top in several locations, two per side.
The best thing for this is the clip on the end of a small animal leash.
They're strong, easy for people to open, and hard for fuzzies to open.  You
may be able to buy just the clips at a hard- ware store.  Good luck!!!
 
                        CHERYL
[Posted in FML issue 1274]