Inspired by rensho's suggestion, I installed a couple pieces of Velcro to secure my mud guard to the swing arm. I am not sure if it will work - the Velcro doesn't stick too well to the swing arm. I don't know if that is because it is so cold in my garage, or if it because of the rough surface.
I also noticed that there were a few wear marks on the guard caused by my D606 tire - probably during the few times I hit around 70 mph. My guess is that the wind blew the guard back into the tire, so if this Velcro sticks, it may just solve the problem of tire wear.