During a deposition, you are sworn to tell the truth and risk perjury charges should you not do so. The rules of evidence are pretty lax during a deposition as the intent is to find out information ... and you can be brought before the court if you refuse to answer quetsions. The best advice to follow during a deposition is to listen carefully to the question asked - and only answer that which was asked. You do not have to offer information that was not directly asked of you. If the quetsion calls for a yes or not answer, you respond yes or no - not with long statements or stories. if the questioner wants the story, make him ask for it!
Hopefully the wife's attorney will speak wiht you beforehand and prepare you for what youwill go through as well as represent your interests at the deposition. You are, of course, free to retain and have present, your own attorney if you chose to do so.
The key is to tell the truth - but only tell what was asked of you.
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Please note that these comments do not constitute legal advice. It is always recommended that you consult with a local attorney, who can explore all the facts and issues of your specific situation and then advise you of any legal rights and remedies you may have under the current laws of your jurisdiction.