Sweet Jesus you want to suffocate your chickens? You are so wrapped up in killing them humanely but you want to poison and suffocate them? Dear God!! And as far as stunning the only reason to stun then slit is to help blood drain better. That's the only reason for stunning. And really if you are so poor you HAVE to raise your own chicken meat you better have about 10 acres for rangers or raise about 10,000 cornish and sell most of them because that's the only way you will beat supermarket prices on chicken meat. If you go small scale you will have to sell most of what you raise for about double supermarket price just to cover your expenses don't expect a profit. I've found the best way is to simply lop the head off and let them bleed out. Just use a nice heavy axe with a sharp blade. Good luck.