have you checked out this list of pet friendly apartments in the area?
The Original Pet Lovers Companion Magazine | Area Northern-virginia Apartments-pet-friendly
also, you could try Virginia Equestrian (Virginia Equestrian.com - For Rent Classifieds)... probably a bit less likely to find something there, but horse people and dog people tend to be one in the same, so you never know! I don't know how far north you want to be in Virginia or what your budget is, but saw a few listings in Culpeper, one each in Centreville, Lorton and Manassas...
The Original Pet Lovers Companion Magazine | Area Northern-virginia Apartments-pet-friendly
also, you could try Virginia Equestrian (Virginia Equestrian.com - For Rent Classifieds)... probably a bit less likely to find something there, but horse people and dog people tend to be one in the same, so you never know! I don't know how far north you want to be in Virginia or what your budget is, but saw a few listings in Culpeper, one each in Centreville, Lorton and Manassas...