I'll bet dollars for dimes that you need to use a larger piece of foil. It should wrap around the bowl and almost to the neck at least. The way the foil stays in place is through friction. It needs to be tight and have a large surface to surface contact area to stay in place. Watch my videos about foiling a bowl and it will show you what I use to great success. Also, sealing the bowl with a little of the juice fro the tobacco can help make a better seal.