Sheepdog Tip of the Day, Before Combat tip 303
If you can't carry a gun, consider a pepper gel such as http://www.amazon.com/SABRE-RED-Pepper-Gel-Professional/dp/B004NKSPR8/ref=sr_1_1?ie=UTF8&qid=1438739148&sr=8-1&keywords=sabre+pepper+gel . it has a steady stream for a long distance, doesn't spray indiscriminately, and is better than nothing. For a teacher in a school who doesn't have the option of carrying a gun, it can have a significant impact on the individual coming to harm your children, possibly giving them to chance to slip past the attacker and escape.
Lt. Col. Dave Grossman, The Bullet Proof Mind seminar (paraphrased)
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Other killology services:
Bullet Proof Mind for the Armed Citizen Seminar
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Additional Resources
For PTSD, Shepherd Resource Group.