Woodsie,
In Virginia we're never 100% sure about any public areas, but I doubt it. I can't tell if Fort Ward is a national or state historical park, but either way, you'd probably get arrested. I can tell you that if it were OK to hunt Fort Ward, it would be pretty well picked over by now.
It is tough to find any place in Arlington or Alexandria (other than private property) to swing a detector. Arlington has "rules" against detecting in public parks, but NOT "laws" - so you might get run off but you won't get arrested. In Alexandria it is a class 2 misdemeanor if you are caught detecting public property.
That said, you never know what will come out of the ground in Northern Virginia. I've found CW bullets in modern school yards and other relics in small patches of woods near my house (near Dulles airport). If your daughter lives in one of the older neighborhoods, I'd start in her yard.
Good luck.
DCMatt
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