A Daily Double bet can be high risk and high reward. The payouts can be huge if you can choose two winners that aren't favorites. You can mitigate risk by introducing wheel bets that allow you to include multiple selections in one or both of the races.
The Martingale strategy involves doubling up on losing bets and reducing winning bets by half. It essentially a strategy that promotes a loss-averse mentality that tries to improve the odds of breaking even, but also increases the chances of severe and quick losses.
