Recently I lost my license plate while riding off road. I got torn off in a crash. So, I cam up with a solution that will fix that. A clip on and off license plate.
I used one of the mounting brackets from the Hero digital camera pack and the baseplate of the package. I'm sure if these are not accessable to you, you could find another way. When you hit the dirt you can just take it off and put it in your pack or something. I put mine in the webbing on the outside of my backpack so that even if I have to hit road in between trails the fuzz won't mess with me.:ride:

Good idea...is it solid? in other words any chance of it coming off on it's own? does it rattle?

very solid and does not rattle and I don't think it will come off!:ride:

I plan on using screws to attach the part to the license plate. I was even thinking of making a aluminum backing plate for the license plate to make it even stiffer.