Drunk driving is a very serious charge and, understandably, many people think that those who are accused of the the crime are guilty before they even go to trial -- or before the criminal process even truly gets going. However, there are certainly effective ways for people who are accused of drunk driving to build a defense that holds water.
For example, the way the police arrested you, or how they went about the criminal process, could have violated the law. Maybe they didn't have probable cause or improperly stopped you when you were arrested. Maybe the police didn't follow protocol throughout the investigation, or the evidence against you was tainted some how. Or maybe the accuracy of the tests they performed (breath test, blood test or field sobriety test) or the results of those tests are called into question.
Then there are circumstantial cases to be made. For example, what if you drove drunk to prevent a "greater evil," such as to save someone who was having a medical emergency? What if you were forced to drive drunk under threat of violence? What if you were entrapped by the police, or you were involuntarily intoxicated (such as someone spiking your drink)?
Drunk driving defenses are no guarantees. Such is the way of the criminal justice system. But that doesn't mean they can't be effective. Those who are accused of driving under the influence of drugs or alcohol need to defend the charges against them because they carry very serious consequences.