In Ross v. Ross, 149 Wis. 2d 713, 718, 439 N.W.2d 639 (Ct. App. 1989), the Court employed the estoppel doctrine to prevent the modification of payments under 26 U.S.C. 71, which are created by the tax code permitting nonmodifiable limited term periodic spousal support. The parties' stipulation provided for maintenance of $ 733 per month for sixty-three months. The Court observed that stipulating to a nonmodifiable maintenance provision is a calculated risk that could well have turned out to the disadvantage of either party. See Ross, 149 Wis. 2d at 720. The Court concluded that the agreement did not contravene public policy and, because the four conditions outlined in Rintelman v. Rintelman were met, the trial court properly denied relief.