There will always be good cops and bad cops as long as human nature takes a part in law enforcement. Obviously we trust the good ones and not the bad. I think therefore that certain precautions are necessary to prevent the bad ones from exploiting their power. There have been significant advances in technology that have helped us, such as video cameras and smartphones but there is one factor that I feel is even more important. That is the right to own guns.
The second amendment was intended to protect us from an abusive government and I think that the interactions between citizens and police are the frontlines of this whole concept. Cops are less likely to harass any random stranger if there is a chance that they are carrying a gun. The mere fact that guns are fairly prevalent in society keeps cops on their toes when it comes to enforcing the law, and thus helps to hinder abuse.
The police have a difficult job of being REQUIRED to enforce the law, even when they themselves don't want to. This can put some unwanted negativity in their direction which generates some fear of the 'long arm of the law'. We need a country where the police are not afraid to enforce the law but should be afraid of stepping outside of its bounds. Increased monitoring of the police with modern technology can help us in many areas of the country but the strongest universal response is the right to bear arms.