Maryland DUI defense is similar to criminal defense and even civil trial work in that one has to be careful when determining what witnesses to put on the stand and what they will say. In DUI defense, generally speaking it should be a rare occasion that the defendant takes the stand to testify on his own behalf. The reasons for that are 1) defendants have the absolute right not to testify in court with the judge inferring nothing negative from that decision and 2) when a defendant does testify it gives the prosecution the opportunity to ask him a variety of punishing questions which more likely then not gives the impression to the judge of guilt rather than innocence. The way to protect against this line of questioning is to not have a defendant testify at trial.
Another interesting nuance concerning who testifies in court and who does not is that the focus of the trial will be upon the testifying party(s); thus when the state puts on its own witnesses such as the arresting officer and that officer is cross examined by the defense, the focus of the trial will be upon what that officer did/did not do during the stop/arrest. It will be less upon what the defendant may have done.
Expanding on the defendant testifying in his own defense or even at sentencing, aside from realigning the focus of the case back upon himself, there is frequently the concern that the defendant may say something that is unwise, illogical or untrue under fire of cross examination. Once that mortal sin has been committed, there may be little chance that a successful defense can be resurrected from the ashes.