Manning advocated trail protection and maintenance for much of his life, based on his extensive experience in the Washington outdoors (having backpacked since the 1930s). He was the bane of mountain bikers in the Seattle area. Manning believed foot traffic (both the boots and the horseshoe variety) cannot coexist with the greater speeds of bicycle enthusiasts and disdained local politicians beholden to wheeled-recreation advocates for spouting pure Lycra. Largely as a result of his efforts, Cougar Mountain is off-limits to bikes and even Tiger Mountain has very limited single-track mileage where bikes are permitted.