Regarding the anti-fatigue mat method etc.
The cheaper alternative (if your ramps will allow it), is to wrap a piece of carpet around the bottom rung, doubling back on itself - this way the car tire is on the carpet, which in turn holds the ramp stopping it from being pushed away.
There are ramps out there which have a flat/level portion before the incline to replicate this.
You could always bolt something to the floor to stop the ramps moving if you always use it in your garage or something - you get the idea, use your imagination.
My personal preference is to use speed. If anyone has ever seen the movie 'The Italian Job' - the original one with Michael Caine, where they practice stopping the Minis on a stationary ramp - that's what I do!!!