Okay so my roommate's 6 month old border collie/ chihuahua / rat terrier mix has been bouncing off my butt while I"m walking. I have no idea how to correct this. She does it kind of randomly, although most of time its when she excited about something. I walk down stair and head toward the kitchen and she runs up behind me, leaps into the hair and punches me in the butt with at lease 3 feet, then lands and goes and does something else. If I just ignore her when she does it she continues to bounce, if I just stop and/or turn around she goes and plays with the other dogs or leaves the room. And the other night she actually bounced off my shoulder blades

. Granted I"m only 5'3" but still. It's very annoying and I'm not sure how to correct it, cause she only does it when I'm not paying attention, and obviously my back is turned so I can't see her coming. Any suggestions?