My Dog is a scavenger!

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I have a dachshund/Chihuahua. I can feed her and then 10 minutes later she'll be rumaging through the garbage. She will do this all day. She is also a dog we found from the pound where she was found out on the streets. So that could possibly be the problem also but it annoys the crap out me of. And she know she's in the wrong. If I leave the room for two seconds she beelines it for the garbage and when I'm coming back I hear her running back towards the couch. It's funny but I still hate it. Is this just a dog thing. Do all dogs do it?