Chicken Woes

So for those who didn't know, my family got some chickens over a month a go.  At first we didn't have a pen for them and one of the chickens escaped and got eaten.  One other got smothered in her sleep by a bigger chicken.  So we built them a pen.  We let them out all day.  Everything was fine. For about a week.  Then a cat got in and ate four of them.  So again we started only letting them out when we were watching.  Yesterday, Dad spent all day enlarging the pen and electrifying the top so when cats would climb, them would get zapped.  We get home from church and there is a cat in the pen over the body of a dead chicken.  Back to the drawing board.  We can't put a top on top of the cage unfortunately...