(a) Number of Jurors. A jury shall be composed of twelve members, but at any time before verdict, the parties may agree in writing with the approval of the court that the jury shall consist of any number less than twelve or that a valid verdict may be returned by a jury of less than twelve should the court find it necessary to excuse one or more jurors for any just cause after trial commences. (b) Waiver. A defendant may waive his right to a jury trial only with the approval of the solicitor and the trial judge. (c) Protection of Right. In all cases, the trial judge shall ensure that the defendant's rights under the state and federal constitutions to a trial by jury are preserved. This replaces Circuit Court Rule 46. The language is based on Rule 23, Fed. R. Crim. P.