Hi, 

I think the important point is that there are different manifestations of violence in society. I believe that everything starts from education and that is the long term solution. Will that help right now? absolutely not but investing time in anti violence programs for teenagers and raising awareness towards these issues is a key move in fighting violence.

I don't really believe there are easy solutions for complicated problems and violence is definitely that kind of problem. In the short term qzmaster591's idea sounds good. I would also try to enforce higher security standards in clubs. I don't mean that police need to be present at all times but a serious search for weapons and dangerous objects can certainly be conducted. 

But as I said in the beginning EDUCATION, EDUCATION, EDUCATION!!!

All the Best.