Some inconvenient facts
There have been more incidents of police officers killing unarmed black men since July 17 of this year than there have been incidents of police officers being killed by unarmed assailants in the past three years.
Police homicides made up less than 1 percent of all occupational fatalities in 2012 (the most recent year for which the Bureau of Labor Statistics has published occupational fatality data), and police homicides by personal weapons [i.e, hands and feet] made up .02 percent of all occupational fatalities. 2013 saw as many dog bite-related fatalities as police officer firearm-related fatalities. The facts remain that occupational fatalities for police officers are rare, occupational fatalities due to homicide even rarer, and occupational fatalities due to homicide via personal assault so rare that no serious argument can be made that its statistical incidence requires constant vigilance.
A study funded by the Center of Disease Control tracked the number of fatalities caused by cattle in Iowa, Kansas, Missouri, and Nebraska between 2003 and 2008. There were 21 such fatalities. That means that there were two more fatalities caused by cattle in just four states over a six year period than there were law enforcement officer deaths caused by homicide using personal weapons over an 11 year period nationwide.