Tenure or Renewable Contracts?

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After viewing the video from NBC regarding teacher tenure i leave with a somewhat confused view about teacher tenure. I believe tenure is a great way to make teachers feel secure about their careers and not have a looming consequence constantly on their shoulders but i also feel some teachers take advantage of tenure. As they said in the video many teachers see tenure as a way to relax and this may cause teachers to not put in 110%. But many states now are seeing that many teachers aren't performing at the correct levels so a few states are adopting "renewable contracts". These renewable contracts offer teachers a two year contract, but the teacher is subject to performance evaluations. I feel that this is a great way to make sure teachers are on top of their game and are making sure they put in 110% at all times. Although this is a great way to make teachers become more consistent with their teaching i feel that without job security for teachers they may go into work with a bad attitude reflecting it on their teaching then the students suffer. Also the video states this costs even more money and documentation then before and the overall reason for this is to save money. As future educators what do you guys think? Should we use renewable contracts or tenure?