You can't prevent a player from clicking GO BACK. He can always revert an action if he don't like the result and try another.
More importantly, there is no reason to prevent a player from doing that. Remember: you are not competing with a player, but helping him have fun. If some player gets more fun by trying all the links, then let him do it!
If you want players to stick with their first choice, the best thing to do is to make a page with this advice before the game.
Removing the back button with a hack is wrong, annoys players A LOT and no one should ever do it.