The 35-year-old former Torquay United player made 13 appearances during his loan spell with the League One side as they successfully avoided relegation.
Town manager Keith Downing told the club's official website: "I'm absolutely delighted to have Alex on board with us.
"He was a big influence on our recovery last year and his experience will be invaluable to us. Alex has a strong desire to prolong his career and I'm sure he can play a major role for us over the next two years.
"Alex had a couple of other options to join different clubs and that shows how highly regarded he is. Hopefully his decision was swayed by his time with us last season.
"He knows how we work, how I like to work and I know he enjoyed playing a part in our survival. We're all keen to push on and move the club forward and Alex wants to be part of that."