What is the test for objecting to the giving or the failure to give an instruction?

Federal Rule of Civil Procedure 51 states that "[n]o party may assign as error the giving or the failure to give an instruction unless that party objects thereto before the jury retires to consider its verdict, stating distinctly the matter objected to and the grounds of the objection." This court has interpreted the rule strictly and requires a formal objection unless the trial court is aware of the parties concerns with an instruction and further objection would be unavailing. Glover v. BIC Corp., 6 F.3d 1318, 1326 (9th Cir.1993).