How do I get my dog from eating stuff off the ground when I take her for walks?

We have a two year old American Staffordshire terrier and she has responded well in most regards to treating her with a treat when she does good things.. but when we go out for walks she just wants to sniff and eat things off the ground.. I would really Iike for her to get over this behavior. She finds like chicken wing bones and weird things that I don't even see… I've tried taking treats with me and pulling her away and saying like leave it! Then giving her a treat but it's been like 2 years and she still eats stuff off the ground sometimes. I can say she does leave trash alone like paper and wrappers and stuff but if there is something food or some weird interesting thing she is going to eat it…her tummy gers upset easy. It would be better if she didn't eat stuff off the ground outside.. .. ..