Why does my dog eat everything outside?

I have heard that dog that eats everything in sight can be due to boredom. I would make sure that your dog has plenty of exercise and even work to eat toys to keep his body and mind busy. My dog does eat every piece of food in the backyard or on the street. I have taught him the command "Leave it" which helps a good deal, however, I still need to be proactive in looking for food scraps on the ground before he does.