WORK on ownership, accountability and strengths. Hold a meeting and, as a team, agree that no one will ever say anything behind each others backs which they would not say to their faces.
This is a given, and must be accepted on an emotional level. If everyone simply nods, they will not do it. If anyone suggests they are already doing this, just ask them if there is anyone in the team that they do not particularly ‘get on with’. If they say ‘Yes’, ask them what happened when they shared that with that person, in private. People must buy into this at an emotional level. Everyone must buy into it.