Ad-hoc networks are expected to play an important role in future commercial and military communications systems. As such, scalable routing strategies capable of supporting greater user mobility and a wide range of applications are needed. This paper proposes a novel routing metric, which defines a probabilistic measure of the availability of network paths that are subject to link failures caused by node mobility in ad-hoc networks. It is shown how this measure can be used to select more stable paths and reduce the routing overhead caused by node mobility. A mobility model is first proposed and used to characterize the movement of ad-hoc network nodes. This model is then used to derive expressions for link and path availability. Finally, simulation results are reported which validate the proposed analytical model.