Are there ways for the enemies to reduce the accuracy of a system

The only way to divert a bomb is to make a decoy. This would involve using whatever it is that the bomb is attracted to being fired away of the target so that the bomb hits the decoy instead. This method is commonly used in air to air combat and submarine warfare. When a missile is detected, a decoy is released and sometimes the missile or bomb hits the decoy. What types of systems have been proven accurate-----How much do systems cost?