
When I first saw this idea, I found it really unique but weird. After much later did I realize it was nothing new but a rather popular sport by many countries all over the world. Snail racing is a sport that involves two or more land snails.
The Snails
Find them in your garden or grass patch lands. During rainy days they are abundant all over the fields and gardens. Find them and leave them in appropriate environments like flower pots etc. Remember to leave sufficient grass and leaves to feed them!
The Race Board

It can be just a simple round board with two rings. The inner ring contains the snails while the outer ring marks the finishing line for the race. You could leave some grass or leaves to attract the snails to head towards the finishing line.

You need to label the snails in order for people to identify them. This could be done simply by using a colored sticker or perhaps you could paint a number on their shells. You could also name your snails!
Fundraising Tips
There are many ways you could do this. But becareful not to turn it into some sort of illegal gambling den and get into trouble with the law. Check your local law guidelines for a better idea.
One way would be that you could sell coupons for people to support a particular snail. Those people betting on the winning snail will win a prize. Another idea could be the pay out would be tokens instead of real cash. The tokens could be used at any other stalls in the fundraising event.