At the 1968 Summer Paralympics held in Tel Aviv, Israel, Marson was proclaimed the outstanding athlete of the Games after winning ten gold medals; three in athletics field events, three in swimming and four in wheelchair fencing. His swimming golds all came on the same day as he won the 50 metres events for freestyle, breaststroke and backstroke. In wheelchair fencing he won individual gold for épée, foil and sabre. He was joined by Giovanni Ferraris, Vittorio Loi, Franco Rossi and Germano Zanarotto to defeat France 5-4 in the final and win gold for Italy in the team foil. With Ferraris and Zanarotto he won a silver in team sabre and also won silver in the team épée alongside Loi and Rossi. He successfully defended the Paralympic javelin and discus titles that he had won in Tokyo and added a third athletics gold medal in the club throw and a bronze in the shot put.