FWIW just leaving the FD on and lowering it a bit works like a charm keeping the chain on. Dog fangs in my experience have been problematic. Of course the inner and outer guard rings are the best. I had an old chainring that I ground off the teeth on to use as a guard once. There is another seat tube mounted chain guard called a Jump Start which is suposed to work quite well. You can see it here:
http://cyclocrossworld.stores.yahoo.net/chainrings.html