Until recently, ad hoc networks were mainly used for military and security-sensitive applications. Nowadays, they could also be used in SOHO (Small Office / Home Office) or home networks. In such networks, devices are linked by long term relations. To ensure their security, it is necessary to define precisely which devices belong to a given network and are consequently inside the security perimeter. The chosen mechanisms need to be easy to use, because the users of SOHO and home networks are neither willing nor able to configure the security of their network. In this paper, we present a new fully distributed approach for securing long term communities of devices in SOHO and home ad hoc networks that minimizes user intervention.