The ultimate solution of course is Christ. Belief in Christ and living by Christian values would prevent death and destruction caused by human hands.
The death and destruction we are now dealing with was precipitated by men, not only acting outside of, not just Christian values but also the rules and values of law enforcement in Minneapolis, Minnesota. I see two possible solutions for stopping the potential death and destruction caused by legitimate, legal protests getting out of hand.
One possibility would be to, at the first act of criminal aggression, spray the protesters with fire hoses. This would be nonlethal, very discouraging, and would have the added benefit of knocking out the thousands of cell phones the protesters are using to photograph or video the activities which they use to encourage others to amp up the destruction and looting.
The second method would be to face the crowds of protesters with a sufficient number of law enforcement officers to discourage criminal activities. The first individual to break the law should be immediately arrested and removed. If that did not deter a second, and third, they should be handled the same way, all the while making sure the masses are made aware of this activity. If this method of crowd control is not sufficient, tear gas, pepper spray and rubber bullets could be used. The main thing is to not allow things to get out of hand, or as Barney Fife would say, “you got to nip it in the bud.”