Do we have to put armed guards at our schools?

On the 13th of September of this year this whackjob with a grudge of which nobody can be certain as towards whom, except perhaps humanity itself, walked into Dawson college and began firing his semi-automatic weapon on the innocent students that happened to be in the room before moving up to the next level of the school where the police confronted him and he subsequently off'd himself(the coward). A couple of weeks later in Bailey CO. this mentalcase of fifty someodd years went into a highschool and (according to reports which I don't doubt) violated a half dozen young female students before killing one of his victims and then himself. This week charles carl roberts(his name doesn't deserve caps) went into the Amish schoolhouse in Nichol Mines PA and executed 3 of twelve girls between six and twelve years old of which two more have perished so far bringing the death toll to five. Being a dad of a 7 year old daughter and a 4 year old son I'm getting a bit nervous about the safety of my kids. Both of my kids are in institutions that require numeric passcodes to enter the buildings they are still vulnerable in the playyard or when parents go to pick up or drop off their kids.
Do we post armed security at the main enterences of schools or do we lock our kids down after we drop them off until we pick them up?
I want my kids to be able to play outside during the fall. I want them not to be always looking over their shoulders. Society has an obligation to protect the innosence of the young from the screwed deviance of the ....not so young. If some gill or roberts or whoever has some gripe and voices it. Should it not be on the person who heard it to alert the authorities and have these sickos locked up before anyone ever gets hurt or killed. I know if I knew someone was talking about his gun collection and the fact that he hated men or women.....red flag 911. I hope that as a society we can figure out how to reign in the domestic terrorists as well as the foreign ones so that maybe our kids can play in the park.