Is a defendant entitled to be instructed on his theory of the defense?

"A defendant is entitled to have the judge instruct the jury on his theory of the defense, provided that it is supported by law and has some foundation in the evidence." United States v. Mason, 902 F.2d 1434, 1438 (9th Cir. 1990). "A failure to give such instruction is reversible error; but it is not reversible error to reject a defendant's proposed instruction on his theory of the case if other instructions adequately cover the defense theory." Id. We "review de novo the question of whether the district court's instructions adequately cover the defense theory." Id.