Staff writer tackles five key issues the Dallas Cowboys need to address this offseason.Issue No. 5 -- Deciding whom to re-signThe Cowboys believe they've built a team that's primed for success for years to come. They primarily feel that way because of their young, talented offensive line and Pro Bowl rookies Dak Prescott and Ezekiel Elliott.But keep this in mind: Thirty-four percent of the players on the roster are set to become unrestricted free agents in March.The Cowboys have 18 players who will be free to sign with other teams in an offseason when an increased salary cap could drive up the price tag for average talent.The Cowboys must decide who among the group of 18 is worth re-signing.Four of the Cowboys' top defensive backs are entering free agency: cornerbacks Brandon Carr and Morris Claiborne and safeties Barry Church and J.J.