Secure external acces (VPN)
The only solution to let clients control there home externally in a secure way is using a VPN.
The are plenty of routers on the market that act as VPN gateway to the local network. Be wary of the cheaper products because the VPN throughput is usually quite low. Also some manufacturers will supply their VPN routers with some sort of licensing scheme based on the number VPN connections allowed. You should also consider the fact devices that use multicast \ broadcast packets may not work unless otherwise specified by the router. Even if they do say that there is no guarantee without testing. Typical example for this would be UPNP based devices, so Sonos, Apple TV, iTunes (Bonjour based).
Customer support service by UserEcho