Here are two reviews that show a connection between exercise and bone density and the probability of fall related fractures:
The effects of progressive resistance training on bone density: a review. - Abstract - Europe PubMed Central
Over the past 10 years, nearly two dozen cross-sectional and longitudinal studies have shown a direct and positive relationship between the effects of resistance training and bone density.
Exercise interventions to reduce fall-related fractures and their risk factors in individuals with low bone density: a systematic review of randomized controlled trials - Springer
Exercise can reduce falls, fall-related fractures, and several risk factors for falls in individuals with low BMD. Exercise interventions for patients with osteoporosis should include weight-bearing activities, balance
I haven't read all of these papers yet (but I will!) but it seems that exercise, especially weight bearing exercise, is more important for maintaining bone density than consuming dairy or calcium supplements.