After the war, Denecke moved to Portland, Oregon, and joined the firm of Mautz, Souther, Spaulding, Denecke & Kinsey in 1947. The firm is now known as Schwabe, Williamson, Wyatt. While in private practice Denecke argued in front of the U.S. Supreme Court as attorney for Ross Island Sand & Gravel in a worker's compensation case, "Hahn v. Ross Island Sand & Gravel Co.", 358 U.S. 272 (1959). During this time he served as a member of the Portland School Board in the 1950s. Denecke left the firm in 1959 when he was appointed as circuit court judge for Multnomah County by Governor Mark Hatfield.