Duxbury arrives at the Blues from National League North side Spennymoor Town.
The left-back, 27, was part of Stockport County’s title-winning side of 2019.
He has also enjoyed spells at AFC Fylde, Chorley and Boston United.
Leitch-Smith, meanwhile, arrives at Gorsey Lane after a stint with Northern Premier League rivals Nantwich Town.
He made 16 appearances in all competitions for the Dabbers, scoring twice.
The 32-year-old was a product of the Crewe Alexandra academy, and went on to help the club secure promotion to League One via the play-offs in the 2011/12 season.
He has accumulated over seven years of Football League experience for a range of clubs, and also featured briefly in Scotland for Dundee.
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