Depositions are different than regular court hearings because the gathering is of an intimate nature. Just the necessary attendees are allowed to participate. However, this does not mean that you cannot be surprised by the presence of someone else. That person might or might not actually be allowed to participate.
When it comes to expert witness attendance to depositions, Peter Kent Consulting highlights the most important attendance rule that has to be respected. This states that both parties and counsels can attend the deposition. Others can attend but the court can state something else. The affected organizations or parties are allowed to move for a protective order that can exclude some designated people from a deposition. This is not possible when referring to parties affected by discussed actions, their counsel, and officers.
What we should highlight is that depositions are based on a practical approach. Because of this, in most cases, we only see some parties participate. This includes the deponent, the examiner, the counsel of the deponent, the counsel of other parties, the videographer, the interpreter when needed, and the court reporter. The goal is to guarantee the safety of the deponent so that any deposition is truthfully offered.
When it comes to expert witnesses, they can attend the deposition, unless the court denies this for whatever reason. This can be done if the other party can offer a good reason for this to happen. Besides this, we can only talk about the situations when examiners want to have nonparties participate. This can include consultants and expert witnesses. This is usually needed to assist when it comes to follow-up questions or there are some additional inquiry areas that might be pointed out by the third party as being very important. When the nonparty appears at the deposition, it is possible to refuse the proceedings until a person leaves but that is very rare and can only be the case if a very good reason is given for such a desire.
To put things as simple as possible, you cannot realistically stop the deposition in the event that you are surprised by the presence of a third party, like an expert witness. This is only possible when there is a court order that you can use for this. However, you are allowed to ask for the deposition to be suspended in order to apply for the court order that excludes an expert witness. This is commonly done by attorneys so that they can use the services of more favorable witnesses.
When you are the party that invites the third-party, like the expert witness, you do not want to be faced with the situation in which people appear and the deposition is suspended because the opposing counsel looks for the protective order that excludes the invitee. Save the inconvenience and simply notify the other counsel that an expert witness will participate and that the protective order motions need to be made in advance before the deposition happens. When you do this, the opposing counsel cannot counter the decision you made.