Generally speaking, it is not a good idea to try to represent yourself against any criminal charges.
Drunk driving may seem like a relatively minor offense, but it is in fact one of the more complicated criminal charges for prosecutors to bring.
There are many technical defenses that an attorney may be able to raise, to assist you either in avoiding conviction, negotiating a lesser charge, or in reducing the consequences of conviction.
There are several common defenses, including the following:
Incorrect or Inadmissible Test Results
A defendant may argue that the blood alcohol test figures used by the police are incorrect or inadmissible due to error in the administration of the test. Sometimes, for example, the testing device was not properly maintained (or the maintenance records are wrong), or the officer who administered the test is not properly trained. Sometimes the police will violate their own procedures when something goes wrong during testing - such as failing to observe the suspect for the appropriate time before administering the test, or failing to call a supervisor in response to an error message despite a policy requiring them to do so. Failure to give proper "chemical test rights" warnings may also result in the exclusion of the test results. Also, it may be argued that certain medical conditions or medications inflated the test results.
Lack of Probable Cause
A defendant may argue, on a number of grounds, that the police did not have probable cause to arrest him for drunk driving, and thus that any alcohol test results should be suppressed (kept out of evidence in court) on the basis that they result from an illegal arrest.
Somebody Else Was Driving
A defendant may argue that somebody else was driving - for example, that he changed places with the real driver, because the real driver was very drunk and he thought he was under the legal limit. The prosecution must prove that the defendant was driving. However, this is a difficult defense to raise, as usually the defendant is seen by the police behind the wheel of the car, and has previously admitted that he was driving.
There Was No "Impairment"
A driver may present witnesses who testify that they observed him driving shortly before, or at the time he was pulled over, and that they did not see any sign that he was "impaired" in his driving ability. It is possible to argue this defense without witnesses, but it is difficult, as police officers tend to be very convincing witnesses.
Rising Blood Alcohol Content
Sometimes, a defendant may argue that he was not "above the legal limit" when he was driving. He may argue that he consumed liquor right before he drove, and that the alcohol had not yet been absorbed into his blood. (Depending upon your stomach contents, it can take as long as three hours for alcohol to be absorbed into the blood, so a person's blood alcohol content may continue to rise even after he stops drinking.) However, during the time between the traffic stop and the administration of the blood alcohol test, that alcohol was absorbed, resulting in a misleadingly high test result. Most states allow the use of a "preliminary breath test" (PBT) result, taken at the time of arrest, to rebut the "rising blood alcohol" defense - if the PBT result is the same, or is higher than, the "official" test result, it tends to indicate that the person's blood alcohol was not rising, or was in fact falling, prior to the official test. (PBT results are not ordinarily admissible, in most states, except in very narrow circumstances such as in response to this claimed defense.)
With the rise of medical marijuana laws and increased abuse of prescription medications, some states have passed laws that effectively criminalize the driving of a motor vehicle when traces of certain potentially intoxicating drugs can be found in your system. Whether or not it's legal to use, a prescription medication or a controlled substance, a blood or urine test showing the past use of a drug may potentially be used as a basis for an impaired driving prosecution long after the driver is sober. It may be necessary to introduce medical or toxicological evidence, and to also assert constitutional defenses such as the claim that these laws violate a driver's Due Process rights, when fighting this type of charge.