Sniffing requires access to the media or the network in some way. The BEST WAY to prevent sniffing, is to prevent access. Encryption will exposes an attack surface, since the intruder has somehow managed to access the network. Encryption protocols such as WPA2 prevents unauthorized reading of data as it crosses the network. While restricting physical access and registering/limiting the machines that can run on the network do help , this is the immediate answer for sniffing prevention. The "best" answer is when given only one choice is encryption. Restricting physical access to a network while leaving the WLAN in protected is useless. The best answer not provided is to restrict physical access and use encryption.