I'm assuming we're talking about desktop games -- something the player downloads and runs on their local computer. Many are the memory editors that allow you to detect and freeze values, like your player's health.

How do you prevent cheating? What strategies are effective to combat this kind of cheating?

I'm looking for some good ones. Two I use that are mediocre are:

• Displaying values as a percentage instead of the number (eg. 46/50 = 92% health)
• A low-level class that holds values in an array and moves them with each change