In Final Fantasy VII, how do I win the Magic Counter materia at the Choco Races?

I actually started playing this game when I was about 17 (I'm 28 now) and still have not finished it because I want to collect all the materia before I do so. I haven't played it in years but still have my PS1 for the sole reason that I will finish it at some point!

I can never get the 'Magic Counter' materia though, I know it's a prize at the Choco races but no matter how many times I bet on races or race I never win it.