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There really isn't a way to do that. Nothing that happens in the civilian court would legally bind the military in any way, because they are separate legal jurisdictions. So, if you were to manage to go to court, challenge the DUI, have it dismissed, that wouldn't stop the military (if it wanted) from taking its own legal action to separate you. They don't have to have a conviction in a civilian court to do that.
So, while it is certainly in your best interest to get a local defense to mitigate the civilian charges, there is not method that the defense counsel can use to actually hinder the military from whatever action it might choose to take.
Now, all this is predicated on the idea that the military finds out. If they don't find out and choose to take independent action, then certainly getting this case dismissed or reduced is in your best interest. My point is just that there is no method to ensure that nothing can be done by the military. Everything depends on whether or not they discover this issue.
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