Dear local stray cat:
While I would pay good money to see what you would do if you actually got one of the chickens, I don't recommend it. They're bigger than you, have claws, and there's 4 of them. They'll hold you down and beat you up. I suggest you consider an easier target -- say one of the local wedge-tailed eagles. You only escaped the loving attentions of the Demons today through sheer dingdangity luck.
If you find a cat in your pen, you have my full permission to take any action you like. Just remember, fur is bad for the digestion and that cats have a fairly impressive turn of speed. Also, there's a dog on the other side of your fence, but she likes to sleep under the house. Make sure you cluck loudly so she's got a decent warning before you herd the feline over.
While your valiant attempts to break the world land speed record on the way out the back door are admirable, you've only just recovered from your paw injuries. Might I suggest you slow down slightly before we have to deal with a permanent injury? Also, the cats have a head-start on you, plus a wire fence between you and them. The chances of you actually catching them are nil. Shall we settle for banging the back door open, while barking madly, then proceeding to the fence at a decorous trot that does not endanger life, limb, and the sound barrier? You are free to woof to your hearts content.