A terrific career between the sticks has seen Clarke represent Oxford United for more than six seasons, as well as spells with the likes of Bristol Rovers, Northampton Town, AFC Wimbledon and Eastleigh.
Following the departure of Brendan Moore, United boss Kevin Nicholson has turned to an experienced high-quality gloveman for the campaign ahead.
“I am delighted to secure the services of Ryan, a proven goalkeeper at this level and levels above,” said Nicholson. “He provides a big voice and a commanding presence for those around him.
“He is fine all-round goalkeeper and in such an important position on the pitch. Ryan was the outstanding candidate in a strong field of goalkeepers I interviewed. We are all very happy to welcome Ryan to the club.
“He had a stop-start season last year and has shown a determination to come to a club where he can play, develop and lead. He fits all my criteria for character and attitude, which, as always, is the number one quality I look for in recruiting players.
“I can’t wait to get started with day one of pre-season”.