Unfortunately, Minimum Defense Frequency is considered by many Hold'em players to be too difficult to understand or use at the table. It's not that hard, it can improve your win rate, and it can easily be used at the table.
Take a simple example. You are playing heads up, there is $10 in the pot, your opponent folds 50% of the time, you always bet every hand for half the pot, and the dealer hates you and deals only blank cards to you.
This is actually a very profitable situation for you and easy to understand. When your opponent folds, you win $10. When you loose you loose $5. Your Expected Value is $2.5 on each hand.
So how does this relate to MDF.
EV = (win $ * % win) – (loose $ * % loose)
EV = (5) - (2.5) = 2.5
You win 2.5 (on average) every hand.
MDF = pot / pot + bet
MDF = 10 / 10 + 5 = 66.6%
In the game described your opponent needs to call or bet 66.6% of the time to prevent you from exploiting him. See, it's not all that hard to understand and it works. It does not replace exploitative play but can easily be used with it. You can do both and it's not all that complex.
Think about that for a minute. Using MDF against an opponent with the wrong fold frequency, you win with blank cards. Imagine if you got real cards and had the best hand 50% of the time.
MDF is the fraction of your range that you must continue with when facing a bet to prevent your opponent from profitably bluffing any two cards. To calculate MDF for your opponent: it's important to know that with the correct MDF you can not be exploited by your opponents bluffs. Really, it's that simple.