I've had that experience. Completely locked up the wheel and pitched over forward and sideways in the middle of a major intersection racing the yellow. I was pretty careful not to let my chain get any more slack than necessary (a little slack is useful if your chainring isn't properly centered) but it was still enough to throw the chain.

A few ideas:

1. Keep your chain tight.

2. Get track nuts. These will let you wrench down the driveside especially without having the wheel walk forward in the ends. Without track nuts, you can get the chain just so and then when you're spinning that wrench to the right, the nut will pull the wheel just a bit forward. An alternative is to get a chain tug (if you have track ends... I suspect a little mangling could get one to work in horizontal dropouts, but I'm not sure), but you'll spend more on the tug than the nuts.

3. Inrease you chainring size. With a larger ring, it takes more slack to be able to get the chain all the way off. 40/16 is a pretty small gear anyhow. Now that you're stronger, why not step up? Between 44 and 47 might feel better.