This one was by far the deepest relic I have dug. It's been about a month, but I would have to estimate it was close to a foot down. I almost gave up digging. Not sure why I like this so much. I do believe it is very old though.
That looks like a military piece. I have a WWI ring that has that same Eagle or very close to it on it. Did you find it near a possible WWI training site or old military installation by chance? I have found lots of old military stuff and I would not put that one being an old military letter opener. Any markings on the back?