What kind of mammal is this?

Today makes twice I have seen this critter running around my house here in Maryland. but neither time have I got a good enough look at it to identify it. It is grey in color sleek body line with a short tail. it is not a cat. nor is it a raccoon or a gopher or ground hog it ran way to quick for that. to small to be a fox to big to be a squirrel. reminded me of a ferret but was bigger and it did not run like a ferret. could this be an otter or a weasel? or maybe something else? give me your ideas or a way to identify it so I can look it up. thanks